Ok, I realise, I need to do some reading here. 
You mean in general?
That seems to be the case! 
$ ls -l /var/lib/pacman/sync
total 49348
-rw-r--r-- 1 root root 45 20. May 2023 community.db
-rw-r--r-- 1 root root 45 20. May 2023 community.files
-rw-r--r-- 1 root root 133747 18. Mar 15:15 core.db
-rw-r--r-- 1 root root 1038167 12. Jul 2023 core.files
-rw-r--r-- 1 root root 21528 18. Mar 17:23 endeavouros.db
-rw-r--r-- 1 root root 152432 13. Jul 2023 endeavouros.files
-rw-r--r-- 1 root root 8761017 19. Mar 00:41 extra.db
-rw-r--r-- 1 root root 40035949 13. Jul 2023 extra.files
-rw-r--r-- 1 root root 143564 18. Mar 00:23 multilib.db
-rw-r--r-- 1 root root 217131 12. Jul 2023 multilib.files
This seems to be a start:
A Complete Idiot’s Guide To Endeavour OS Maintenance / Update / Upgrade
So that means my updates/upgrades have been potentially incomplete and this system was sitting on a time-bomb which went off 8 days ago?
This seems to be the explanation why all our efforts to downgrade/re-install packages didn’t help.