My command wants me to get my appointment history of all appointments I’ve had and give it to them, do I have to provide it? is it legal?

That's not usual for command to do, so something else is going on. Talk to your ADC

Appointment history is just when you had appointments. Where and when and who. No PHI or PII issues there because it wouldn't disclose your personal medical history. If you are on a medboard get support from your medboard case manager , unit limdu coordinator and also your Unit Medical Officer. They will help keep the Command updated on what they are allowed to know and what they need to know.

It is par for the course because some of those that came before you sometimes were known to abuse the system. Making sure you are going to legit appointments is normal because people have scammed in the past. Don't take it personal. I was a SSgt going through a medboard and had to deal with the same BS.

Yes your command and a civilian boss can ask you for your appointment history, it is not protected medical history to know when your appointments were.