Entra ID retires memberOf on 3 November: after that date, membership stops being recalculated
Message centre post MC1448379, published on 5 August, has been read as a deadline. Read it the other way round: if you run a memberOf rule in production, you already have the problem it describes, and the preview documentation says so in a paragraph almost nobody reads. What happens on 3 November is not an outage or an error: memberships stay "in their last known state". That is where licences, Conditional Access and Teams membership hang from.