The real problem is the lifetime tenure of the justices. The Founders did that for good reason, to insulate the Court from the immediate politics of the time. But people are simply living longer now, and Republicans figured out how to ratfuck the Court to stack it in their favor. (Helped in no small part by RBG, who could not be convinced to retire at the right time). Openings on the Court are so rare that it is worth expending significant political effort to get them to go your way.
If Democrats ever get control of the Presidency and Congress again, they should immediately move to blow up the Court to 13 members. They can do it by immediately turning it up to 11, and then making it 13 two years later, in order to stagger the changes. But this is important enough that they should blow up the filibuster to do it.
(13 is a magic number because it matches the number of Federal district courts.)
And then, after the bill is passed, they should work with Republicans on a framework to add term limits to the Constitution. Each of the 13 justices gets a 13 year term, each justice could serve up to two terms, consecutive or not, and would have to be re-appointed and re-confirmed for their second term. They can even tie the number of justices directly to the number of Federal circuits, so that it is harder to ratfuck on the future. 26 years is long enough to insulate a justice from politics. And out of our 116 justices to date, only 28 have served more than 26 years.
But by giving every President the right to nominate one justice per year, it makes the process more regular, and the political payoff for engineering a single appointment becomes less attractive. Supreme Court turnover becomes a predictable thing.
At this point, Republicans may be willing to support that amendment, because the alternative would be for President Newsom to appoint 4 Liberals to the court for Life in quick succession, and wait for their own full control to ratfuck it again. That might take a while.