Yes. I think Breyer wanted to write some more minority opinions and embrace being the most senior liberal justice before deciding to retire in June 2022. Breyer knows that if he doesn’t retire it could be catastrophic. However, I think replacing Breyer will be the only Supreme Court justice appointment Biden will get to make.
Yeah I don’t see how Biden gets another appointment after Breyer unless Dems somehow held the Senate in 2022 and something unexpected happened before the 2024 election (when Dems would likely lose the senate due to the class that is up then).