Cannot assign folder permissions in mixed hybrid environment i.e. cannot grant a M365 user calendar permissions to an On-Prem 2016 mailbox or vice versa.
john@contoso.com is the calendar being shared
scahill@xyz or dirk@contoso.de is the person who is being granted permission
Get Existing Permissions
Get-MailboxFolderPermission -Identity john@contoso.com:\Calendar
If user is not English speaking get calendar or other folder local name using
Get-MailboxFolderStatistics -Identity dirk@contoso.de -FolderScope Calendar
Get the existing permissions using the local calendar name
Get-MailboxFolderPermission -Identity dirk@contoso.de\Kalendar
Grant Edit Permissions
Set-MailboxFolderPermission -Identity john@contoso.com:\Calendar-User <alias> -AccessRights Editor
Grant Manage Permissions
Add-MailboxFolderPermission -Identity john@contoso.com:\Calendar -User scahill@xyz -AccessRights Editor -SharingPermissionFlags Delegate,CanViewPrivateItems
Note -SharingPermissionFlags is cloud only
Grant Free/Busy Permissions Only
Add-MailboxFolderPermission -Identity john@contoso.com:\Calendar -AccessRights AvailabilityOnly -User scahill@xyz.com
Grant Read-Only Permissions
Add-MailboxFolderPermission -Identity john@contoso.com:\Calendar -AccessRights Reviewer -User scahill@xyz.com
Grant Limited Details Permissions
Set-MailboxFolderPermission -Identity john@contoso.com:\Calendar -User normilg -AccessRights Editor – scahill@xyz.com -SharingPermissionFlags Delegate,CanViewPrivateItems
Remove Permissions
Remove-MailboxFolderPermission -Identity john@contoso.com:\Calendar -User scahill@xyz.com
Calendar Sharing Rights aka Access Rights
Author: CreateItems, DeleteOwnedItems, EditOwnedItems, FolderVisible, ReadItems
Contributor: CreateItems, FolderVisible
Editor: CreateItems, DeleteAllItems, DeleteOwnedItems, EditAllItems, EditOwnedItems, FolderVisible, ReadItems
None: FolderVisible
NonEditingAuthor: CreateItems, FolderVisible, ReadItems
Owner: CreateItems, CreateSubfolders, DeleteAllItems, DeleteOwnedItems, EditAllItems, EditOwnedItems, FolderContact, FolderOwner, FolderVisible, ReadItems
PublishingEditor: CreateItems, CreateSubfolders, DeleteAllItems, DeleteOwnedItems, EditAllItems, EditOwnedItems, FolderVisible, ReadItems
PublishingAuthor: CreateItems, CreateSubfolders, DeleteOwnedItems, EditOwnedItems, FolderVisible, ReadItems
Reviewer: FolderVisible, ReadItems