This may affect a few more people here.

I'm running SW 2020 SP1 (because SP2 has a problem). Windows updates installed on shutdown yesterday.

Simulation became very slow on certain operations, like redrawing a mesh or simulation result.

I first reinstalled display drivers [nVidia Quadro K2200], for no effect.

Checking the new Windows updates, I uninstalled the most recent general Windows update, KB4532693. All is good now.

So it may be very configuration specific, but in case it helps thought I'd share.