Usually the app takes some time to detect and load the videos. Try this:- open the Videos folder in the File Explorer app. And play any one of your videos from there. The video will play in the Films & TV app by default. This might trigger the app to load those videos. Then open the Films & TV app and wait for a few seconds or maybe a minute. The videos might appear. This has worked for me many times. This trick even works with Groove for me. Also make sure those videos aren't hidden.
If this doesn't work then you may hard reset your phone, since you cannot uninstall the Films & TV app.