Time & Date KCM can not store settings on a non-systemd system
Which is interesting, as the desktop variant of it works fine. First guess would be the lack of systemd on this system, as it's postmarketOS, but seeing the desktop part works fine seems to make this not be true.
The console reports an error.
Failed to set timezone "org.freedesktop.DBus.Error.ServiceUnknown" "The name org.freedesktop.timedate1 was not provided by any .service files"
A quick internet search suggests systemd provides this but openrc-settingsd can too. However, I don't have that installed on my desktop, so it shouldn't be required.
Edited by Bart Ribbers