Regarding the fcitx issue, someone I think is a KDE dev did a bit of detective work and posted this explanation on Reddit.
SDL2 wrongly has fcitx5 set as a build dependency in the Arch package due to a packaging mistake (sdl3: fcitx5 is not needed as a make dependency (!1) · Merge requests · Arch Linux / Packaging / Packages / sdl3 · GitLab). Trying to compile the package will install fcitx5.
This was likely caused be the confusing SDL documentation on this (Remove unnecessary fcitx's devel package dependency in linux doc by wengxt · Pull Request #12372 · libsdl-org/SDL · GitHub). You don’t actually need fcitx5 to build SDL2.
The SDL2 package was replaced by a compatibility package and the original SDL2 was moved to the AUR (After update, keyboard layout settings now get reset at every restart - #2 by scotty65).
Packages being moved this way confuses pamac, even though the old package isn’t necessary anymore, it will still try to build it from source from the AUR because it doesn’t know yet that the package isn’t needed anymore. (Please make the upgrade process a two step process: First upgrade repo packages only, then upgrade AUR packages · Issue #488 · manjaro/pamac · GitHub).
So if a user had SDL2 installed, the AUR enabled, and did not use an automatic tool to clean build dependencies, a combination of minor flubs and weird interactions would lead to fcitx5 being randomly installed on people’s computers.
Plasma has nothing to do with it, we’re not involved here at all (except that we could do a better job of telling people that fcitx5 is active). We just get the blame in the end.
I’d be interested in people not on Manjaro where this happened though.