How To Activate My Windows 10 Pro Without Product Key

If the key is genuine and not used on another PC (or the old PC is dead), it will usually work. Microsoft calls this a "free upgrade" loophole for accessibility.

Activating Windows 10 Pro Without a Product Key: A Technical Overview how to activate my windows 10 pro without product key

This pulls the license from the cloud onto your new machine. If the key is genuine and not used