Clock widget in panel doesn't show anything

Hi - are you able to share your system info from the Info Center application?

Also - what you’re describing seems possibly related to the situation in this past thread - Plasma 6 Does Not Display Time - #18 by Pink3 - where the issue was timezone data and settings being somehow messed up in an Arch Linux installation, and required some packages to be reinstalled and systemd services to be reestablished. That thread might be worth checking out?