Thanks for reaching out, Jack8094.
It sounds like you're having some trouble with video playback on your iPad. We can help.
You mentioned this is happening with videos you receive in Messenger. Do you mean Messages, or a third-party app like Facebook Messenger? If it is a third-party app, try downloading the videos to your iPad and playing them from Photos instead. If the issue goes away, you might want to use these steps to see How to contact an app developer for support for third-party apps.
If the issue remains, and you're noticing brightness to be the main factor, you can check your iPad's brightness settings here: Adjust the screen brightness and color on iPad.
Give those steps a try first, and let's see where things stand.
Keep us posted.