Hi,
Reactivation after replacing the motherboard depends on your original license.
Was Windows preinstalled on your old computer, or did you purchase a retail license separately?
If you have the original retail product key, try Settings > System > Activation > Change product key, ensuring the installed Windows edition matches your license.
If your digital license was linked to your Microsoft account, try Activation > Troubleshoot > I changed hardware on this device recently, then sign in with that same account.
Preinstalled OEM licenses are generally tied to the original device, a motherboard replacement may require a new license.