Hi - the answer to this might depend on what types of actions you’re looking to add. A lot of information on this topic was summed up in a post from earlier this year:
If all you want is to have templates for your Office suite…
In your home folder ( ~/ or /home/yourusername ) you should see a Templates folder. That’s where you’d create new templates usually that appear in the right-click context menu under New File.
On Plasma, there are two requirements to make it show up in the context menu: a file with the format you want the template in, and a .desktop file. You’re right that on other environments you can just dump a file there.
So for example if you n…
Is that what you’re looking for?
Edit: the link here might be relevant as well: Creating Dolphin service menus | Developer