there may be a way to get around this without disabling all embedded videos. i would have to check out the details, but as long as the videos are not embedded using youtube’s embedding template thing (because i’m assuming it loads client side tracking scripts or does similar datamining fuckery) it should be fine. that’s something that can be investigated more, but changing the referrer policy has absolutely no downside and should really just be done now. that way at least the issue is mitigated for conventional links.
edit: it occurred to me that if <video> tags work on discourse you can probably do the embedding through an invidious instance or even just linking directly against the googlevideo url instead of the youtube embed. btw i did also check what gets loaded when you do a normal embed and i was right, tons of tracking scripts get pulled in (it doesn’t even seem to use the referrer header but that also might just be my browser config). i’ll have to poke around when i have more time, because i don’t actually know how discourse works in this aspect.
edit2: for now, if anyone reading this absolutely must embed videos, make sure you click the “enable privacy enhanced mode” box in the youtube share/embed thing. or, alternatively, just change the url in the html you paste in to use “youtube-nocookie” instead of “youtube”. i don’t know how much this actually does, but it will at the very least prevent simple page loads from phoning home. how much data gets leaked by actually loading/playing the video is anyone’s guess.