When I do a right click on an entry in Folder View (in every mod: as desktop widget, in a panel or as desktop mod) also a left click is performed and the file/folder is opened. The bug is found in Plasma 5.8.5 and KF5 5.30 on Manjaro Linux. I tested it on KDE Neon dev-unstable and everything is OK.
That was fixed for 5.8.6 (and 5.9.0) which is why it works in neon unstable but not in 5.8.5 shipped in Manjaro. *** This bug has been marked as a duplicate of bug 360219 ***