We are using Office 365 but the meeting room is a shared resource between multiple companies with different policies, so we need to support Apple iCal, Gmail etc.
As far as I have understood, publishing a calendar will not let users edit it (or at least make new appointments/edit their own appointments)? In this case it's meaningless, since everyone has a right to book the meeting room, regardless of whether you are part of our organization or not.
One option seems to be handing out guest access to the shared resource mailbox using our Azure AD, but when I try, I can't give editing permissions to calendars even to the guest users?
Perhaps using Office 365 in this case is pointless? It seems designed for large corporations, not smaller companies working tightly and sharing resources with other small companies.