I switched from Manjaro XFCE to Manjaro KDE a while ago (installed KDE beside XFCE) and always had weird issues with Thunar and now Dolphin.
As an example, I occasionally download versions of GE-Proton from github and am not allowed to copy them to the recommended (hidden) steam folder compatibilitytools.d . My workaround is to do that with a sudo-launched instance of Thunar, because I am not allowed to run Dolphin with sudo.
On another machine with a later install of Manjaro KDE I have no issues to move files with Dolphin.
I guess it is some type of missing user rights, but I cannot figure out what is wrong. Can anybody trace this down?