SUMMARY
If a window has a window rule that specifies a virtual desktop, and you open the app on a different virtual desktop, it will move itself to the desired desktop as it is supposed to. And on X11 it will also show up in the correct virtual desktop on Pager. But on Wayland it will show up in Pager on both the desktop you opened it from, and on the target one. It will stay like that until you close the app, or move the app to the desktop you opened it from, and then back to a different one, only then you will have just one occurrence of an app in pager.

STEPS TO REPRODUCE
0. Be on Wayland session
1. Set an app/window rule that specifies a virtual desktop at app start.
2. Start an app from a different desktop than previously specified

OBSERVED RESULT
The app will appear in Pager on 2 virtual desktops

EXPECTED RESULT
It should appear in just the target one, where the app is actually opened. As it is showing up in the first virtual desktop but it is not actually there.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Solus 4.3
(available in About System)
KDE Plasma Version: 5.24.4
KDE Frameworks Version: 5.92.0
Qt Version: 5.15.3

ADDITIONAL INFORMATION
Has been like that for a few months I think.