We have a Group Calendar called ResourceDevelopment set up and everyone has access to it, however, only the person who created an entry seems to be able to edit their entries. Even setting everyone as an “owner” of the calendar doesn’t seem to solve it. I’ve tried to find a way to edit the Calendar Permissions but it will not let me access it. Are you able to help me sort through this by chance? Is there any way for me to edit these settings? What seems to be an issue is that no one can edit anything on the calendar other than the original author. I’ve made them all “owners” of the calendar through the Group but it doesn’t seem to be helping ☹.
Toying with folder-level permissions for a Group mailbox is not supported afaik. You can change them via PowerShell, but not all clients "respect" the changes. I'd recommend using a shared mailbox if you need to customize permissions.