DueSlotPlanner's iCalendar feed was retired
In January–February 2026 Microsoft retired Planner's “Add plan to Outlook calendar” iCalendar feed (Microsoft 365 message centre MC1193421), and said there was no replacement.
If you used that feed to see Planner due dates in Outlook, the subscription stops updating. DueSlot is a third-party app by Nostello OÜ that creates a calendar in your own mailbox and keeps events there from your Planner tasks.
It is not a Microsoft product and it does not restore the old feed. It uses Microsoft Graph with your sign-in, on basic plans only.