Check Media for Compatibility

I understand that before we upgrade to Catalina we need to ensure all the movie files we have are compatible and that conversion needs to happen before we move on from Mojave.

There is an option in iMovie in Mojave which we can select: File>Check Media for Compatibility.

A lot of my video/movie files are in the Photos app not in iMovie.

How do I ensure all the video files in the Photos app are going to be okay in Catalina? They will need to be as I may want to use them in iMovie at any point in the future.

Do I have to import all the files to iMovie and then in iMovie select File>Check Media for compatibility?

If I do this what will happen to the movie files in the Photos app

Thanks, Peter