There does seem to be a bug on Oculus Quest. In Yum's comment at the top of the thread, you said "Settings in IMAGE ADJUST (brightness/contrast/saturation) can be only saved per individual video." Unless I'm doing something wrong, these settings are not saved per individual video. If I watch a video, go back to home screen then open up the video again, the individual image adjust settings revert back to zero / default.
Would be awesome to have a customisable default image setting, then if you tweak any settings for individual videos, they are remembered in perpetuity. I'm hoping this is fairly easy to implement? Otherwise, loving the app.