Hello, @RavenWolfie. It's very strange that, despite ensuring that you have the correct settings in place, you aren't hearing your ringtone or the message notification on your S21.
I understand that you have already gone through some steps to identify and resolve this. Please can you let me know whether you've had the chance to go through the steps below (from our friends at Samsung US)?:
I'm interested to see how you get on with these.