I noticed lately that watching some Youtube videos full-screen results in a noticable flicker. I don't see a flicker viewing the same videos on the same machine with Mojave's Safari.
Here is a video capture from my (very old) phone:
Note that Stats for Nerds needs to be off and I've only noticed the flicker in full-screen mode with the player controls hidden (i.e. with the cursor off to the side so they autohide). The flicker appears to be some interaction with the autohide/autodimming.
I have not seen this flicker when viewing the same content with Orion under Catalina but that's also a different hardware/configuration (retina laptop screen versus external 1080p TV)
I expected the video to play in full-screen similar to Safari on the same machine and generally with no flicker not in the content.
Version 0.99.128.2.1-rc (WebKit 619.1.11.111.2) Build date Aug 4 2024 Mac mini (macOS Mojave 10.14.6 build 18G9323)
Mojave (10.14)