Gnome-shell indecently using resources

Even when idle top reports gnome-shell using 50%-95% CPU. I had this problem previously, which I solved by removing various extensions, but now it’s happening again and hindering my system’s usability.

Is there any way to see what is making gnome-shell so suddenly resource hungry?

Removing outdated/unmaintained extensions would be a start. You may create a new “test” user account and see if problem persists, that means it’s a package-level problem and needs dev attention.