How to recover a windows 10 product key from linux
How to Recover Windows 10 Product Key on Ubuntu
Remove the hard drive from the old computer and mount it in ubuntu
sudo mount /dev/sdX /mnt/{$SomeFolder}`
Install hivexget
sudo apt install libhivex-bin
Move to the mounted drive
cd /mnt/{$SomeFolder}
Recover the key
hivexget Windows/System32/config/SOFTWARE '\Microsoft\Windows NT\CurrentVersion\SoftwareProtectionPlatform' BackupProductKeyDefault