Hi! Whether you can use your existing license on the new build depends on the license type. If your current Windows 10 Pro is a retail license (or a digital license linked to your Microsoft account), you can move it to new hardware and activate Windows 11 Pro without buying another license. After the motherboard/CPU change, install Windows 11 Pro (you can choose “I don’t have a product key” during setup), sign in with the same Microsoft account, then go to Settings > System > Activation > Troubleshoot > I changed hardware on this device recently and select your device to reactivate. You can also enter your 25-character Windows 10 Pro key under Change product key, Windows 10 Pro keys activate Windows 11 Pro of the same edition. Ensure the new motherboard supports TPM 2.0 and Secure Boot to meet Windows 11 requirements.
If your current license is OEM (preinstalled on the original PC), it’s tied to the original motherboard and generally can’t be transferred; in that case you’d need to purchase a new Windows 11 Pro license for the new build. Replacing only the GPU or CPU usually doesn’t impact activation, but a motherboard swap will trigger reactivation. If you’re unsure of your license type, run slmgr /dli in an elevated Command Prompt to check the channel (Retail vs OEM), or review your purchase documentation.