pcmanfm root permission error

[kqlnut]

This is probably due to you running a Wayland environment (as opposed to X11). Phosh and Plasma Mobile both run on Wayland. Here it says a root instance is not possible under Wayland (but "admin mode" is). I never tried pcmanfm or bothered with trying to open graphical applications as root (which is also not recommended because of various security implications), so I cannot give you more specific help. But you could try fiddling with the hints given here to maybe make it work with Wayland.

(E-mail notifications on this forum are known to be quite buggy unfortunately.)