Hi! Your actual Windows license is stored either as a product key or a digital license associated with the device and (sometimes) your Microsoft account, not your Microsoft 365 subscription.
Whether you can move your Windows 10 license to a new Windows 11 PC depends entirely on the type of license. If the old PC came with Windows pre-installed (OEM), that license is legally tied to that hardware and can’t be transferred. If you bought a retail key (boxed copy / Microsoft Store), you can usually move it by installing the same edition on the new PC, signing in with the same Microsoft account, then using Settings/Activation/Troubleshoot/“I changed hardware on this device recently” to reassign the digital license from the old machine to the new one. If that doesn’t work, it’s almost always because the key is OEM/non-transferable, the edition doesn’t match, or it was never properly linked to your account.