Hello danamikejohn,
We see you're having issues with being able to crop videos on the Mac, and we can help.
This page here will have details on how to get that accomplished: Change and enhance a video in Photos on Mac
It may help to try fully closing the app (Command-Q, or Photos > Quit Photos), and relaunch it.
Another step would be to try restarting the Mac, which can help with odd issues that may come up.
You can also try testing the issue out in a new Admin user on the Mac, which helps to isolate it down to being a user-specific or system-wide issue: Set up users, guests, and groups
Cheers.