Can I set up a user in my Entra center that has access to other user's resources?

Question

I am using microsoft graph to sync SF & outlook events and toDoTasks.

However, app level permissions are not available for toDoTasks.

I've managed to sync everything using delegated permissions when it comes to syncing these records from SF to Outlook.

The other way around is a problem.

I'm using webhooks, but the auth troubles me. SF uses Guest Users for this purpose. I can give the guest user (that 1 specific guest user, there are no multiple) access through authentication. I authenticate him to use the graph api with my user, so the webhook updates work only when they come from my outlook user, when I switch users I get 'access denied'. This is most likely do to the authentication.

Can I somehow set a "master" user in the entra center and grant him some kind of permission to access other user's resources, so that I can auth him in SF for the guest user and then use him to access the resources?