Explanation
You can set expiration policy only for Office 365 groups in Azure Active Directory (Azure AD).
Note: With the increase in usage of Office 365 Groups, administrators and users need a way to clean up unused groups. Expiration policies can help remove inactive groups from the system and make things cleaner.
When a group expires, all of its associated services (the mailbox, Planner, SharePoint site, etc.) are also deleted.
You can set up a rule for dynamic membership on security groups or Office 365 groups.