Something I've noticed not getting enough attention is the full court press that Republican state legislatures are making for reducing voting access as a result of the Biden win.
Using the "stolen election" myth as a pretext, Republican controlled states across the country are passing restrictive voting laws intended to drive down voter participation. High voter turnout almost always benefits Democratic candidates.
https://www.nbcnews.com/politics/meet-the-press/after-2020-loss-gop-targets-voting-restrictions-n1261080
The current SCOTUS will not overturn these restrictions.
The Biden presidency, despite being generally popular, may very well be the last Democratic presidential victory in the foreseeable future. The Republicans are moving hard to entrench themselves as a permanent ruling minority.
I know I'm quite vocally critical of Biden here, but I'm not entirely sure what, if anything, he and the rest of the Democratic party can actually do here.