When you full screen a YouTube video, exit it and attempt to scroll back to the top, the header bar (Where the YouTube logo and search bar is) is hiding under the Orion toolbar. I have tried across multiple Macs (Though all running the same versions of macOS admittedly) and have been able to reproduce consistently.
This happens with no extensions enabled, any tab configuration and with mini toolbar both on and off. Refreshing the page resolves it until you go full-screen again. This does not happen on Safari or Firefox. This happens whether the video is playing or still.
You can tell the bar goes under the toolbar because when you scroll up really hard you can see the header.
Repro steps:
Open a YouTube Video
Full-screen it
Exit full-screen
The header goes into hiding
Repro video:
The header bar should not disappear under the toolbar.
macOS 15.4.1 (24E263), Orion 0.99.132.0.3-beta
Sequoia (15)