Really two options:
Remove the subject for the room for all meeting requests:
Set-CalendarProcessing -Identity <room> -Deletesubject $true
https://learn.microsoft.com/en-us/powershell/module/exchange/set-calendarprocessing?view=exchange-ps
OR:
Set-MailboxFolderPermission -Identity ******@contoso.com:\Calendar -default -AccessRights AvailabilityOnly