This is a good question.
It would be nice to have a player that plays every format. LLs vPlayer is a nice one, but it also fails on certain H.264 encoded files. (Maybe it’s related to this: Can't play h264 video with yuvj422p pixel format) I haven’t had time to take a closer look at this.
Sometimes when i’m away from home, i like to spend some time watching a movie or so. My workaround is to re-encode video files. Another solution is to use Jellyfin server at home. Both available clients, native Sailfin ja Android Jellyfin have worked so far. Except on a train, where 4G is so flakey it’s mostly unusable.