What I also found out is that in the “About-Tab” of the wallpaper engine settings, their are no pythone3-websocket dependencies found.
Since you installed it manually, is the check mark displayed?
As mentioned above, it is possible to install the wallpaper plugin if you turn DUSE_PLASMAPKG OFF, but then the following error appear
I could not reproduce it. I turn DUSE_PLASMAPKG OFF but build works fine and plugin not installed.
What I also found out is that in the “About-Tab” of the wallpaper engine settings, their are no pythone3-websocket dependencies found.
Since you installed it manually, is the check mark displayed?
I was able to reproduce your situation after uninstalling plugin that installed manually, and I noticed that the folder com.github.casout.wallpaperEngineKde in ~/.local/share/plasma/wallpapers/ has been deleted.
I checked and nix had installed it on /run/current-system/sw/share/plasma/wallpapers and KDE cannot seem to recognize.
Finally I solved this problem by adding a small script. I would like to know if there is a better way to add the folder in user .local directory.