Appears to be a regression in the latest RC. I am using the regular default horizontal tab bar.
1) Have one or two tabs opened.
2) Create a new tab (via the new tab button, or by right-clicking a link and picking open in new tab).
3) Notice the new tab doesn't appear in the tab bar
4) Click on the tab bar.
5) The tab bar refreshes and the new tab appears after that click (and not before).
The tab bar should refresh without you needing to click it.
Orion RC Version 0.99.129.4-rc, MacOS 15.2 Beta (24C5089c)
Sequoia (15)