Hi! Generally, a Windows 10 license works on Windows 11. But perhaps the license you had on your old computer was an OEM license.
OEM licenses are installed by computer manufacturers and come pre-installed on computers. OEM licenses are not transferable and expire when you change hardware, such as the motherboard. You probably lost your license when you changed hardware. That's why the version of Windows 11 you're using is 'free'.
- Confirm this by going to Settings > System > Activation.