[deleted] My thought was to first install Solus Budgie, then it shouldn't be a problem to install authentic KDE Plasma. Oh, if I don't screw it up, you owe me a beer.
Well, good luck to you. A world of difference exists between installing Budgie from the ISO and trying to substitute KDE Plasma as the DE on that installation, as @Harvey pointed out in the other thread where you discuss trying to do this.
Installing Budgie from an ISO is straightforward, but trying to install KDE Plasma on that base is difficult or impossible because the two DE's (Budgie/Plasma) have overlapping functions, dependencies, background services and applications that are not meant to coexist with one another.
Solus specifically warns against attempting this in the Help Center, which gives instructions for installing Budgie, Gnome and MATE desktops alongside each other: "WARNING: Do NOT attempt to install ANY other desktop environments next to KDE Plasma Desktop. This scenario is NOT supported and you will be told so in no uncertain terms if asking for support."
Sticking with the beer theme, I think you are embarking on a "Here, hold my beer and watch this!" adventure.