If I go to Configure Dolphin>Services>Add Services and then I install a addon and then go back to the service menu.then I can't see any addon that I installed.
Works fine for me. What particular addon did you try?
(In reply to Nicolas Fella from comment #1) > Works fine for me. What particular addon did you try? Root actions service menu,Kde-Services and Open File manager as Root.
https://store.kde.org/p/1231579/ too
Do you have packagekit-qt5 installed?
(In reply to 2wxsy58236r3 from comment #4) > Do you have packagekit-qt5 installed? With that it works. Why isn't that package installed by default in kde?
That's a question for your distro. :) They're the ones who choose what's pre-installed. For the record, it drives me crazy that Arch-based distros don't pre-install this package alongside Discover. They have their reasons, and I understand them, but I don't agree. For details, see https://bugs.archlinux.org/task/58524.
(In reply to Toadfield from comment #5) When you install a package, pacman will output the optional dependencies (and brief descriptions of their use) of that package. You can also run pacman -Qi dolphin and you will see "packagekit-qt5: service menu installer".