Something wonky is going on, because I just noticed similar behavior with my Pixel Buds 2nd gen, except it's my left bud that's draining quickly (while the right bud is remaining at 100%). I also reset my buds, and it didn't help.
I've also been having more problems recently with the buds connecting even when they're still in the case, which is a problem if I'm trying to use the phone's own earpiece when answering a call. If the buds are actually connected without me being aware, it may seem like no one is on the other end of the call.
I doubt it's an aging battery issue, because I don't use my buds very much.
I sent feedback to Google about this. In the meantime, I wonder if I'll have to bust out the Buds A I just got with my Pixel 6a.