From my experience the RVX Builder (fork and upstream) are very buggy on Android, at least in Android I don’t see why use it over Revancify.

I generally recommend the CLI for those that can use it as well.

I suppose also opening the video file in the browser works for that?

https://github.com/inotia00/revanced-documentation

Try the other Methods in the ReVanced Extended documentation.

Using Revancify is a good option, or you can use the RVX-Builder in a computer.