Hi Vlopddap,
I have run a test on my Outlook for Mac 15.6 and there were no accepted buttons in the room request email first, but after I added the room mailbox into the “People I am a delegate for” option, a few minutes later, the buttons showed up automatically in the Outlook for Mac 15.6
Given this situation, after you added the Supervisor into the booking delegates of the room mailbox in the Exchange Admin Center(EAC)(outlook.office365.com/ecp), please remind your supervisor to add the room mailbox into the “People I am a delegate for” in the Outlook for Mac.
Please note that it will take a few minutes for the changes to take effect.
If I misunderstand your meaning, please feel free to post back.
Best Regards,
Mouran