Hello,
I would like to change my system time to the 12-hour format. I was able to change the panel clock without issue, but there does not seem to be an obvious way to change it system-wide under Time and Date. When I open gnome-clocks or gnome-weather, they are showing the time in 24-hour format. (I am on SparkyLinux (rolling) MATE).
Thanks!
Check here, for example:
https://wiki.debian.org/DateTime