I've been getting "Operation not permitted" errors on some (but not all) files in a particular folder that's synced between Linux (Nobara) and Android. After multiple weeks of grief to trying to track down a fix, I've finally found the cause.
Turns out, Android can't handle special characters like ":" in file names, while the filesystem I have on Linux (btrfs) does. Changing all colons to another character like "_" in the filename prevents the error and allows syncing.
Devs, can you please look into adding a more specific error message for this? It'll likely save multiple people similar amounts of frustration.
Also, I would have preferred to submit the error/change request via GitHub, but that's not allowed, and I don't want to make yet another account just to post on your forums.