Be able to subscribe to calendar events of a group of users. The idea is not about registering to calendars of groups.
Receive a notification at the web-hook listener when a change occurred in a calendar of any user of the group.
The limitation of 1000 total subscriptions per tenant (as outlined here https://docs.microsoft.com/en-us/graph/webhooks#azure-ad-resource-limitations) is a killer for organisations with more than 1000 users as typically with any larger enterprise. This would be an idea to overcome this limitation and be able to react on calendar changes in organisations with more than 1000 employees.
PS: This platform here is a horrible platform to search whether the same idea has already been posted. Please link similar ideas. Also if there already exists ways to achieve the said please also comment.