Liberal Supreme Court Justice Stephen Breyer to retire: reports
He's been on the high court for over 25 years
www.axios.com
So Breyer is apparently retiring come the end of the current term (June). Odds are strongly in favor of Biden getting whomever he decides to nominate confirmed, probably on a party lines vote.
Theoretically, Republicans could kill the nomination but it's highly unlikely that they will. The Senate Judicial Committee needs to vote out the nominee to get them an up/down vote and that Committee has eleven members from both parties, and a tie doesn't advance the nomination. A motion can be made to advance the nominee to the floor ignoring the committee but that would take sixty votes to go anywhere under current rules.
As I said, it theoretically could be blocked but its highly unlikely that it would be.