Overnight travelers can use Night Tube services on the Piccadilly line on weekends

https://www.scribd.com/document/1074929924/National-Rail-to-Heathrow-Routes-Transfers-and-Tickets-Explained-232993

Overnight travelers can use Night Tube services on the Piccadilly line on weekends, or consider night buses that connect to Heathrow’s central bus station.