Video Editing Newbie with iMovie Challenges

I am trying to create a single video using videos taken on my iPhone (13 pro max) and mp4 video files from another source. I am doing this on an iPad Pro 12.9 2nd gen. iMovie keeps making the mp4 video playback darker than it is in the source file if I play the source file on its own outside of iMovie. I have tried adding the MP4’s manually and using the “Magic Movie” but it always comes out the same. There is no way to edit brightness or colors manually that I can find. The options other people seem to have in iMovie are not on my iMovie app. I tried doing it on my iPhone but it’s no better. I just want the MP4’s to play at the original brightness in the source file so they match the iPhone videos and don’t darken the footage. I have never done this before and I am so frustrated. I just want the video to play as it is. Please help. Thank you.