My Samsung Tab S4 is running Android 9 and can generate backup files over 4 GB just fine. exFat is not the only file system used on Android that can handle files larger than 4 GB. My Samsung Tab S4 uses ext4 and I imagine most Android tablets below 12 must use that as well or I would have heard about this more often. You are the first person to report this issue in a very long time, so either the vast majority of users have libraries smaller than 4 GB, users are not backing up their libraries, or most devices are using a file system that can generate files larger than 4 GB.
Mike
Mike