Major New Features:

Programmable buttons

Native web apps
New PDF reader

New

WebKit 616.1.10 (changelog)
Custom toolbar buttons for menu actions #4487 @carl
Native web apps that open in a new window in Focus Mode (Tools -> Install site as Web App #499 @alohaquanhoang
Find text in PDF files (and better PDF support) #278 @piratx
Implement pdf.js #1496 @kzvi
Search invocation keywords should be added to manage search engine #1602 @gabrielchow
Added "copy link" to Tab Right Click/Context Menu #4567 @Itai
Added Safari feature to delete old history items (and downloads list) #1171 @gp
Added (Bookmark/Suspend/Move) Tree menu items
Allow JavaScript from Apple Events #4361 @askingforafriend
Add hint to Window Group switcher if keyboard shortcut is assigned #4354 @phy
Clone sidebar set-up for new window #4342 @mazil
Allow showing more history items in the menubar #2520 @alastor57
Add a downloads option to website settings #3279 @1VbBoIlR9XB3dFKh
Right clicking non-hyperlinked URL should offer context menu option to open link #771 @gp
Add to Reading List added to context menu for links
Site Specific auto-downloads website setting #940 @eirk
Mention RC Releases in Standard "Check for Updates" menu #4501 @Cat
Ability to create new bookmarks using the context menu #4407 @Radev
Added a setting for using accent color in sidebar
Suspended tabs icon #4824 @Longely
Open profile location from manage profile page #4827 @eirk
Suspend Tree #4088 @InTime
Ctrl-a / Ctrl-e shortcuts for scrolling page up/down #4301 @mk_rsa
Pinned tabs in vertical mode should be frozen at the top #1347 @TheOtherKai
Compatibility mode indicator icon or tab styling #760 @Cannabat

Improved

Only show page zoom level if differs from global setting #4505 @eirk
Different icon for private windows #4784 @eirk
Low Power Mode - Tabs with media playing excluded #4971 @styliac
Cant delete selected history at once #4458 @Manan2004
When reseting zoom level, reset to default settings for all websites rather than 100% #4370 @JordanSavoie
Redesign downloads menu + redownload function if failed #4138 @GrasPlukker
Highlighted color wrong for bookmarks library page #4496 @eirk
Drag tab out of window #3379 @amichaeel
Create new bookmark or paste copied one #4636 @TCat
Show The Sidebar Automatically When Focus Mode is Turned Off if it was on Before #4762 @whitemamba
New folder for Bookmarking #4517 @Cat
Update uBlock Origin extension #4707 @joystmp
Compatibility mode menu item name should be static #4803 @eirk
Privacy badger causes Google Drive Upload Fail #4312 @njyo
Add title bar to websites installed as apps #4899 @httpjames
Sort passwords window items #1008 @Fortrikka
WebApps should automatically update when Orion is updated #4911 @laiz
Incorrect capitalization #4802 @eirk
Full Screen creation of new windows #4385 @AshwathSingh
Rearrange website settings into a more logical format #4662 @ForumNinja404
MacOS: Windows don't restore to previous size/location on launch. #4285 @querylous
Right click on profile indicator should show same results as left click #4868 @eirk
Reader mode popup is annoying #2909 @Selector1619
Web app name not bolded in menu bar #4846 @eirk
Web app name incorrect in Info.plist #4845 @eirk
Web app window doesn't get the correct name #4847 @eirk
Webapp breaks Stage Manager #4851 @rosenrot
Web app name not bolded in menu bar #4846 @eirk
Links to external sites don't work in some webapps #4858 @laiz
Discord webapp beeps when typing in the search bar #4857 @laiz
Children tabs not visible after parent closed and reopened #4638 @eirk
Can't delete in-bulk items from my Reading List #3830 @aubreypwd
Make information in "About" dialog copiable at once #4585 @davidkaya
Suspended Tab Symbol #4403 @B4ND1T
"Show History" / "Edit Bookmarks" / "Extensions" etc. should open with the focus on the list of items, not the sidebar #4236 @Avoozl
Option to Remove downloads upon completion #3075 @scottjeffers
Click on zoom level in address bar to reset or change zoom level #4364 @GrasPlukker
Change muted icon #4634 @Longely
BrowserAudit report #3723 @wgdev
Notes tab uses accent color, even when accent color use is disabled #4848 @eirk
Mute This Tab doesn't work on unfocused tabs #4675 @rosenrot
Reduce padding between reader icon and lock icon #4477 @tuesday
WebApps: the context menu option to open in a new window does nothing #4859 @laiz
Bookmark sidebar not being default on reopening orion #4369 @portastar
Clicking on desktop notification should take you to the tab #4616 @AlejandroHernandez
Download size "Zero KB" when download size is unknown #4536 @GrasPlukker
M2 Pro/Max Chips report incorrectly in 'About Orion' #4481 @B4ND1T
Change the look of pdf.js to match Apple design #5002 @Longely
Configure when and where URLs go #4860 @eirk
Programmable button icon selection should be closeable #4963 @rosenrot
Difficult to tell when saved window is inactive #4594 @AlejandroHernandez
Select search engine using query prefix #350 @nhynes
Flashes on waking up suspended tabs #4574 @Gileneusz
Capitalize t in "Open tabs" #4693 @eirk
Library Window small fixes UI
Sortable History & Reading List items

Fixed

Session bug on Kagi, Gitlab (won't stay logged in)
Cannot share Google Docs, Sheets, etc. #4400 @moorejs
Passwords from password provider don't autofill (since 0.99.123.2) #4583 @mb3
Discord logs out when over-extending bookmarks sidebar #667 @Fortrikka
Dashlane no longer fills in credential space after recent update #4597 @bluppen
Closing leaves Webcam on in google meet if using keyboard shortcut. (potential memory leak) #4822 @RaviPatel
KeepassXC-Browser extension's setting menu breaks Orion #4655 @suray
Unexpected animation in tab overview #4357 @Honcharenko
Long YouTube comments don't have 'Read More' option #4042 @laiz
Orion's first use screen not importing stuff from correct browser #4793 @technusm1
Image drag-and-drop starts immediately #4476 @tuesday
Profiles - cannot open primary app profile from dock when secondary app is already open #3433 @frin
Overflow menu shows inactive extensions #4872 @janpeeters
Text box appears cut vertically while renaming bookmarks in compact mode #4810 @amadeusjustinn
AppleScript "make new tab" always creates a tab in the rearmost window #2680 @PhilMac
Applescript creates new tab in wrong window #2531 @robjwells
Website partly freezes Orion #4965 @rosenrot
Closing Bug Icon Menu #4981 @Cat
2 blue bars when dragging tab from one window to another #4414 @Longely
New window without toolbar #4612 @CarlosSilva
Orion RC always launces with the side bar hidden #4709 @laiz
Orion takes any string containing a point as URL #4713 @rosenrot
Vertical tab heading changes appearance on tab close #4775 @eirk
Vertical tab close button is not displayed on hover under some conditions #4235 @Avoozl
Inconsistent x to close tab (again) #4520 @eirk
Show/Hide Bookmarks UI visual glitch #4274 @_I_
Disabling Javascript in a tab also disables Javascript in other open tabs #4798 @mstgrv
Unable to set/change emoji for saved window #4783 @tuesday
Orion RC won't open hyperlinks when it is closed #4819 @GrasPlukker
Scroll & Visual bug on YouTube #4718 @Honcharenko
Images glitching / corrupted and wrongly swapped #4913 @emzoumpo
Content from clipboard not pasted in Wasavi #3590 @purgatori
Website partly freezes Orion #4965 @rosenrot
Toolbar bleeds in with web content after a few minutes of use #3215 @benderrod
Dropdown arrows hangs after moving over with mouse in Settings menu #4735 @Longely
Login page for Aetna.com does not work in Orion #4083 @Jdf3
American Express site loads slowly compared to Safari #3529 @Jdf3
Giantfood.com website does not load #3369 @Jdf3
Video player keyboard shortcuts stopped working in 0.99.123.3.9-rc #5048 @Dustin
YouTube stops video #3293 @scottjeffers
Profiles runs with Rosetta under Apple Silicon #3398 @CyberArchon
Urls with a path become a search #4873 @eirk
History items appear twice in RC #4916 @Longely
Cant play videos on BBC.com without Compatibility mode #4923 @Longely
Develop > "Empty Cookies and Storage for...." doesn't work as expected #4937 @gp
Add Bookmark Folder Crash #5004 @winstonbartlegod
Address bar shows full URL #4754 @GrasPlukker
Lichess.org engine (WASM Stockfish 14+ NNUE) doesn't load #4320 @nherzing
Weird behavior in transformed pop-up window #4724 @Cat
Opening multiple tabs in background causes spinning beach ball #3858 @abayomi185
Tabs from a previously active group aren't cleared from memory #4629 @Stakker
'Close Tree' Button Unresponsive #4739 @jmm6486
Named window keyboard shortcut setting error popup can't be dismissed via keyboard, sometimes gets lost behind other windows.
Kagi logs you out if you don't use compatibility mode #4752 @ushtaritk421
Race condition when calling chrome.runtime.connect and immediately sending message #4011 @comex
Scripting.executeScript not working #3747 @markphilpot
Chrome.tabs.connect disregards frameId #4012 @comex
Ad blocking doesnt seem to work in RC #4918 @Longely
Switching to new tab via AppleScript / JXA segfaults #4438 @jxapplescript
Opening new window window with AppleScript / JXA does not work like in Safari #4439 @jxapplescript
Bookmark Sync in Progress when iCloud Drive disabled #1825 @kilenaitor
Visual glitch when closing the top-level tab in a tree #4757 @Avoozl
This website's UI is broken #4465 @TheUser1
Volume icon stays on tabs after sounds is done playing #4231 @Longely
Kagi session not persisted since last update #4605 @wignercrystal
Downloads sometimes fail when using profiles #3375 @laiz
GitLab redirects to Login #3655 @securemepls
Downward-drag vertical tab placement is always off-by-one
Opening a pdf on the Canvas LMS website causes continuous reloading #4240 @glossary
Google Meet screen sharing is vertical #4225 @nhlushak
Tabs font rendering issue on non-retina screen #2898 @differenceclouds
Page has no tab at all when opening an external link or moving tab to another group #4582 @Stakker
History gets saved from when the history is disabled #4576 @Al
Reader mode checkbox does not reflect the actual state #4584 @davidkaya
Bypass paywall cannot be installed #4538 @Honcharenko
Closing temp window closes active saved window session #4561 @EnderPicture
Search Bar border #4452 @AshwathSingh
Action buttons in overflow menu don't retain there icon, names and are not editable #4972 @janpeeters
Broken site: forums.macrumors.com #4551 @Dustin
Orion incorrectly escapes quotes in headers to WebExtensions #4539 @theLMGN
Orion doesn't remember the last active tab group when launching #4625 @Stakker
With show tab bar enabled on a single tab window, dragging out the tab crashes browser #3948 @EnderPicture
PostMessage with transfer object is broken #4730 @JustinMayfield
Cookies and website data from other profiles appears in New Profile... #4579 @Leirk
Low-priority bug: new tab not showing up, in an odd way #4600 @portastar
URL Overflowing/Wrapping with Linefeed (%0A) #4624 @securemepls
Lost focused tab indicator when tab dragged into tree #4787 @eirk
History menu crashes app if user taps it without an open window & they've not yet tapped it during session.