@leocg You're saying on a normal video, but did you try a live video with fast chat?
I can say this video does it for me (just a popular streamer for reference, not what I usually watch):
https://www.youtube.com/watch?v=nuImMCnkGIw
Opening the video it starts at about ~300 MB, but it quickly creeps up to ~1-2 GB and beyond after some moments in the foreground. While taking screenshots and pasting to a different application, I noticed the memory usage falls down to ~5-600 MB in the background, but it restores its previous usage as I tab back. Closing chat (with the big 'X') stops the tab from accumulating memory, and it will drop to normal levels after a few moments. Reopening the chat starts accumulating memory junk again.
I usually have "dark theme" (top right dots) and "cinema/theatre mode" on (press 't'), as well as "live chat" (not "top chat"). However, the normal "default view" and "top chat" also seemed to be troublesome. It may however take some time to start collecting junk in RAM, and I think I had one instance where I had issues identifying the tab in task manager at all (after which I closed the tab and made a new one, and the new tab was easy to identify again).
I run Windows 10, and I have about 30 other tabs open (mostly news, shops, etc. taking up ~5-30 MB RAM each).