System tray customization?

I’m trying to customize my system tray, but I just keep breaking things. I use KDE as my DE and the system tray as a whole don’t allow any modification(is this supposed to be like that?). I also tried to manually add a network widget, but it doesn’t even appear(because of the sys-net?). Am I stuck with the default or is there a place for customization?
I also tried to install two widgets and Application title - KDE Store
I downloaded the whole gitlab/github and put it under the plasmoids directory, it appeared in the widgets list, but when I add them to the dock nothing happens.