Activating Windows 10 old laptop key for new laptop also brings what to remove the old laptop from the Microsoft account?

So that the key can be redeemed more securely or has nothing to do with it?

A WINDOWS 10 key is bound to the internal PC hardware and recognized by an "internal checksum" with this PC.
It is therefore not transferable to another system.

Hey so I was told that it would work

https://www.giga.de/...-so-gehts/

Yes, the employee could reset this "dongling"; but this is only possible to a limited extent - otherwise 25 other people could use this "trick" to unlock additional devices.