I have bluetooth ear buds and headphones connected to my S21. Since upgrading to Android 12, the pause buttons on both accessories no longer work. Prior to the upgrade, both worked as intended. Now, I need to unlock my phone just to pause.
Have you tried removing them and re-pairing them? I'm on a Galaxy Flip Z3, so should be fairly similar to the S21's update and mine still work both locked and unlocked. Have you tried different music players? (I've only tried Spotify and YouTube)