Comment 8 for bug 1871913

I have found out now that for me the problem occurs only if "Pointer Location" on the "Keyboard & Mouse" page of the gnome-tweaks utility is set. I have turned it off now and the left Ctrl key now works with all keyboard layouts again.

If you happen to not find the mouse pointer sometimes, simply make it bigger, with "Cursor Size" under "Universal Access" in the GNOME Control Center.

See also

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2603