SUMMARY Huion Kamvas 13 Gen 3 (Model ID: GS1333) is not supported or configurable by kcm_tablet despite Libwaom agreeing on its support. STEPS TO REPRODUCE 1. Own a Huion Kamvas 13 Gen 3 (GS1333) tablet 2. Attempt to modify system settings including button configurations OBSERVED RESULT Button configurations are completely absent. EXPECTED RESULT As libwacom-list-local-devices confirms my device is supported (bar minor fixes that are now merged into master), the buttons available as listed by the .tablet file and .svg file should be modifiable using the system settings. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Arch Linux 6.18.0-arch1-1 KDE Plasma Version: 6.5.3 KDE Frameworks Version: 6.20.0 Qt Version: 6.10.1 ADDITIONAL INFORMATION This comes after a saga of trying to get the tablet to be recognized by libwacom at all. Previously it would claim it wasn't supported despite being recognized as a tablet and having a matching PID to the .tablet file's description. Apparently, it was because my tablet did not have the UNIQ udev string that libwacom expected. After that, libwacom-list-local-devices confirmed it was supported. Yet after changing this and rebuilding the libwacom db, the system settings don't reflect the additional support at all. Updating to 6.5.3 didn't resolve the issue.
So, this is kind of an odd situation :-( I do happen to have your same model on hand, so I can confirm this is bug but it's not really our fault. libwacom has no effect on whether the tablet is well-behaving or not (but it does have a minor effect in button detection in our KCM.) Basically the tablet is still reporting its own emulated keyboard inputs, but something else in the stack claims it has configurable tablet buttons. The KCM believes this, and will gladly let you configure buttons that will never be sent, that's nonsense! I don't want to close this just yet though, because I want to think of a better troubleshooting case. If I can't fix or figure out the actual bug, I do want to somehow make sure this incongruity is more obvious in the KCM.
So bad news: there isn't an easy solution to this problem. The tablet will gladly lie to us and there's not going to be an easy indicator that it is. However, for your specific device this will really fix it: 1. Install udev-hid-bpf, there's a package available from the extra repository. 2. Install huion-switcher from here: https://github.com/whot/huion-switcher. There's installation instructions (but unfortunately, no Arch package) but make sure to try it normally first. With those two pieces my Kamvas 13 works, including sending tablet buttons correctly so they can be rebound. Let me know if you have any trouble, otherwise I'm closing this.