The M5s do not function properly on the PS5.
I'm very disappointed. I've been using the M3s for years as my primary gaming headphones but after my second pair started to malfunction I decided to "upgrade" to the M5s. Well, that was a mistake. They are irrecovably stuck in HFP "communication" mode on PS5. Yes, I have done every possible thing to attempt to fix this.
I have cycled every possible audio setting repeatedly. I own an external mic but every time I plug the M5s in they immediately default to that mic. I did find a workaround for getting them to recognize the external mic but it fixed nothing. Support was unhelpful, basically told me "yep that's by design". So yeah, fair warning console users, maybe just stick with the M3s. Debating picking up a third pair although this experience left a real sour impression.