In previous Outlook versions you could subsribe to all calendars of all members of a distribution group, by just selecting it in the address book.
With current Outlook versions this mostly don't work and you receive the message that you have to subscribe to the calendars one by one.
In german this is the error message you get:
The same behaviours also occurs, when you try to subscribe to all rooms at the same time.
To get this working again, you have to disable the "Shared calendar improvements", at least for the duration when subscribing to the calendars.
When this checkbox is disabled, you can again subscribe multiple calendars in one step.
Please be aware, that you should reenable this setting after subscription, otherwise your subscribed calendard will get lost when you have no connection to the server, or working offline.
And a small side note: The GPO policy mentioned in the linked article no longer exists, so don't look for it in current admx templates.
Also setting the mentioned policy registry key seems to have no effect with current outlook versions as of 2022.
There is a new setting for REST communication with calendar server, but this seems to not solve the subscribe problem.
