There is currently no way to set the default sharing permissions for your Office 365 users’ calendars inside the organization. You can create a default sharing policy, but it doesn’t apply to the setting seen in the screenshot above. There are a couple of workarounds you can use. One option is to have the users change the setting themselves, but that’s not the best solution for an administrator. There is a Microsoft UserVoice Poll to suggest the feature.
Exchange Online Shell – Set Default Calendar Sharing Permissions for a Single User
To change the setting for a single user, connect to your Exchange Online Shell and run the following cmdlet (change the options in bold):
This will set the sharing permissions for the default calendar to Reviewer, which will let people inside the organization view meeting details and not just free/busy status.
Exchange Online Script – Set Default Calendar Sharing Permissions for All Users
If you need to change this setting for all users in your organization, you can save this script as a .ps1 file. When running it, you’ll be prompted to enter your administrator credentials to your tenant.
Use caution when running this script as it does change the permissions for all users.