Apple TV

Yes, when signing in with an Apple ID on an older device you will need to enter the code at the end of the password.

However, iMovie theatre is no longer supported so it isn’t going to work no matter what you do.

You will need to put the content into a shared album or import it into iTunes and use hone sharing if you want to view it on Apple TV

What happens when you plug a CAT 5 or CAT 6 connector into the Apple TV and then the other side into the router? Does it work now?

If so, it’s not your Apple ID, but rather the Apple TV itself.

If not, sign out of iTunes. Then sign back in. See where it goes from there.

iMovie theatre is no longer supported

Move iMovie Theater content to iCloud Photos - Apple Support