Welcome to Apple Support Communities. I understand that you're having trouble when trying to create a new project using iMovie on your Mac. I see that when you select to create a new project, you're not seeing a response after selecting "Movie" or "Trailer". I know iMovie is an important application to be able to use and I'd like to help. First, if you haven't already, quit iMovie and restart your Mac: macOS Sierra: Quit apps
If you're still having trouble, I recommend that you use these steps to start your Mac in safe mode: Use safe mode to isolate issues with your Mac
After you've booted into safe mode, open iMove and try to start a new project. If you're able to move past the "Movie" or "Trailer" selection restart your Mac normally and test again.
Let me know what you find.