Icons don't match Applications in Force Quit
A friend's iMac under Big Sur becomes slower and slower. Programs become slow and react only after several seconds. He has tried to call up Force Quit, using the keyboard shortcut Cmd-Alt-esc and was presented with this Force Quit window:
(He uses a Dutch version of mac OS, hence the language.)
Note how the icons shown for Numbers, Safari, and Finder do not correspond to those applications.
Presumably, this is in some way linked to the iMac becoming slower.
Any ideas as to what might be wrong?