Valve is finally changing Big Picture Mode on Steam to something that's hopefully better:
The tweet about the change seems to be a bit premature, as following the instructions does not result in the new UI displaying, and there hasn't been any download updating beta today.
EDIT: The beta update reached me and I'm not playing around with the new UI.
EDIT2: Holy crap, this new UI needs a lot of work before it's ready to be the main UI for Steam. The sounds are obnoxiously loud, there's a whole bunch of menu items that still assume you're running this on a Steam Deck, using the B button to go back shows inconsistent behavior, while I was playing a game the overlay just stopped working.