Everyone has a take on what this means and it'd probably be wise to hold off until Catalist or some other group does a post-mortem on these elections. But my gut tells me that is that all the other stuff - Critical Race Theory, Insurrection, Abortion, etc. - is noise to most people. What it comes down to is that you have a President that is anywhere from 10-12 points underwater on average, and candidates that stood for the Ds last night in the two big races (McAuliffe, Murphy) are going to do around 10-12 points worse than the President did in 2020. It's a more nationalized environment, and it shouldn't be surprising that his unpopularity at the moment is having an impact on fortunes for his fellow Dems.
And I suspect that unpopularity comes down a combination of economic pressures (such as inflation), concern that COVID isn't behind us and/or some fatigue with COVID restrictions, and to a lesser extent Afghanistan (not so much for the withdrawal - but rather that how it played out didn't reflect well on how the President campaigned on competence).
The formula is pretty simple on paper but hard in practice.... if Ds want to at least reduce their losses next cycle, Biden's approval rating is going to have to go up. I think it's possible depending on whether inflationary pressures subside and if COVID increasingly becomes a distant memory in 2022 (I'm more confident in the latter than the former), but who knows. Everything they collectively do as a party though should be done with that in mind. And Biden himself should probably adjust how he is doing his job accordingly as well.