Files app

I am sure if anything has changed with the Files app in iPadOS 15, but you may need to make sure these copied videos are created ( home movie created digital movie content ) .mp4 files that have been placed in the Photos app folder, in the Files app and attempt to play these home videos from the Photos app.

If these .mp4 files are online purchased movies ( digital copy versions ) copied or moved .mp4 movie files may not play on the device due to DRM ( Digital Copyights Management ) protection codes in the data, that will prevent any trasnsferred content DRM movie content from playing.

In the event of DRM protection, you would need to simply download/install this DRM protected .mp4 movie content directly into your iPad and stored directly inside of your iPad.

If these are “ripped” DVDs/BluRay conten from discs, there are ways to get that content working and into an iPad,, but NONE of that can be discussed here, due to Apple having to conform to the Motion Picture's industry DRM rules/laws and, therfore such discussion of copied commercial movie discs is not allowed, in ANY form, here.

You would need to do your own online research on this topic and find your own answers and solution to your commercial digital movies issue.

Good Luck!

Just an FYI,

This is not a chat service here.

Other than someone labelled Apple Community Specialists here, that actually represent and work for Apple, these Apple Support Technical Communities are largely made up of volunteer Apple product users/buyers, just like you.

I and others here, like me, are just Apple product buyers/users here that do not work for nor represent Apple.

Glad your video/movies files issues were all worked out.

Best of Luck to You!

Are these .mp4 video files?