Hello Dismort,
Welcome to Apple Support Communities!
We can help you change the playback speed so your music sounds normal again. See the steps here:
"In the Music app
on your Mac, use Playback settings to choose how to fade songs in and out, change music sound quality during playback, and more.
To change these settings, choose Music > Settings, then click Playback."
This Apple Support page has the full details to help change the speed and resolve the issue: Change Playback settings in Music on Mac - Apple Support
We hope this helps so you can enjoy your music again. Please let us know if you have further questions.
Cheers!