Hi @Bogumil Sekulski
If you have replaced your motherboard and CPU, then you will need to reactivate Windows 10 or purchase a new Windows 11 license. If your Windows 10 digital license is already associated with your Microsoft account, you can reactivate Windows 10 on new hardware. If you want to upgrade to Windows 11, you'll need to purchase a new Windows 11 license. For more information about reactivating Windows after a hardware change, please see https://support.microsoft.com/en-us/windows/reactivating-windows-after-a-hardware-change-2c0e962a-f04c-145b-6ead-fb3fc72b6665#ID0EBD=Windows_10.
You can use Windows 11 installation media to create a bootable USB, and then install Windows 11 on the new hardware. During the installation process, you will be asked to enter your Windows 11 license key. If you've already purchased a Windows 11 license, you can enter the key at this point. If you have not purchased a license, you can choose to skip this step and purchase a license after the installation is complete.
Please note that replacing hardware and changing the Windows version may result in data loss. Be sure to back up your important data before making any changes.
Hope it helps.