I wonder does the subscriptions (Microsoft Graph API) have a limited or unlimited lifetime? Is there any related documentation or guidance available for this... I failed to find one.
Solution
Yes, Subscriptions in Microsoft Graph have a limited lifetime.
For a list of maximum expiration times, see Maximum length of
subscription per resource type documentation.
Apps need to renew their subscriptions before the expiration time. Otherwise, they need to create a new subscription. Apps can also unsubscribe at any time to stop getting change notifications. Clients can create subscriptions, renew subscriptions, and delete subscriptions.