Start a YouTube video (a long video, but that may not be important).
The video ends.
Click the YouTube logo in the top-left corner.
Pick another video and start watching.
After some time, the MacBook dims the display, then goes to sleep and pauses the video.
If, after the display becomes dimmer, I refresh the YouTube page and continue watching the same video, the bug does not repeat.
.
Version 1.0.1 (140), WebKit 624.1.2.19.2, Mac OS 15.7.3 (24G419)
Sequoia (15)