There is a known bug with Android 10 that keeps it from playing MP3 ringtones when the phone rings. It will only beep or set to the default ringtone. The problem is mostly with Samsung and Pixel devices. It has nothing to do with the app or ringtones. Many users are complaining about this not knowing its an issue within Android 10.
Android 10 should be compatible to play MP3 media. Here is the developer docs saying it. Android 10 Media codecs.
How to fix the problem?
The user should contact the devices manufacturer for a patch or update.
Google is working on Android 11 and it should fix the problem.
The user can roll back the device to Android 9. Follow these instructions from Android Authority.