I don’t have specific audio advice, but here are some thoughts on how to troubleshoot a problem.

Since it’s been several hours, you’ve probably already done Step 1 of troubleshooting: reboot the system and make sure an mp3 plays ok.

Depending on your disto, it may make you do manual labor on sound input/output. So go to the distro settings, find the sound settings, and one by one test all the output options. (there’s often a test button that lets you check left and right output)

test the mp3 again (to verify it still does or still does not work)

If you’re getting that far and everything’s working, now start Ubuntu Studio and see if the mp3 still plays ok.

This kind of step by step test, change one thing, test again, change one thing approach will help you figure out which direction to look to solve the problem.