I had that problem initially when I had updated to Gnome 40 using [gnome-unstable] repos to upgrade from a prior version. The lock-up in a gray overview screen issue was annoying but I was able to pinpoint a few problem candidates. I went through the Extension app and removed all of my extensions, then reinstalled only those that are providing a Gnome 40 compatible version. I found that even with G40 compatible extensions, enabling “Window List” and/or “windowNavigator” causes this erratic behavior - as long as I keep those two extensions disabled I don’t have any issues. I use quite a few extensions as you can see below and currently haven’t run into any issues in weeks of daily use:
