Legacy file access is not on, never used it before. And I've cleared the data and reinstalled the app so many times at this point that the only settings I've messed with are the ones that are supposed to (and don't) fix the issue.
edit: I tried @BingBadaBoom's tip, followed by toggling permissions in the app info (settling on allowed). I then went into library settings and specifically selected the Music folder on my SD card. Upon restart, the app loaded fine with all music available without needing to be rescanned. However, after a few restarts and then changing a couple UI settings (I don't like any info showing on the album cover), followed by another restart, the app "failed to load" the files again and everything needed to be rescanned. (None of the permissions were changed by me or changed on their own in the app info)
I'm not disputing that everything is working fine on your Samsung Android 11 phones, but with "fixes" spreading through multiple forum topics (none seeming to last that long) and numerous people still experiencing the same issue, it's clear this needs to be addressed clearly before I waste another few hours on a music app.