motion templates empty

There is nothing to fix.

This folder will be empty unless you add content to it - namely, titles, effects, generators and transitions.

Unless you used to have something there before and now it is not there, it seems that everything is normal.

FCP comes with a lot of templates - these are inside the application itself, not stored in the Motion Templates folder.

The folder is always empty until you put something in it. Do you have a third party plugin to add? It should come with installation instructions.