Somehow, I managed to screw up my system by installing SWAY, and maybe other things.
So I tried a Timeshift restore. First from the Grub menu - yes, I installed the Timeshift Grub add-on, and the Pacman add-on - and then I tried three different snapshots from the desktop, until I finally got back to my working state.
Excellent piece of software! With Btrfs, even better
I am amazed how quick and painless it was to essentially do an OS state bisect.