recover Windows 7 product key from Registry

concepts

• Windows product key
  a 25-character code used to activate Windows.
  format : PRODUCT KEY: XXXXX-XXXXX-XXXXX-XXXXX-XXXX

• Windows digital license
  (called a digital entitlement in Windows 10, Version 1511)
  a method of activation in Windows 10 and 11 that doesn’t require to enter a product key. : uses ==a hidden key== in pre-built installations (oftentimes even in Uefi /bios)

• Windows license

recover

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData

Look for the ProductID under Name in the larger menu on the right.
The Windows 7 product key will be listed under Data.

upgrading

with the prodcut key you can likely upgrade from win7 to Windows 10 for free,
using the product license.