Back when Media players played all YouTube and Twitch videos, at one point Valve broke something that prevented video from being played (including on Steam client and overlay). This is also around when Tower Unite media players went to using Unreal’s default browser.
This was fixed earlier this year on beta and the fix was deployed to the public version on Steam’s end recently. I think it’s time to quickly test if it works again so we can hopefully get the proper media player experience!