Windows 10: can i buy only windows 11 pro product key only without downloading it?

hi,i'm siddhartha from india. i have a desktop running genuine windows 11 pro. i have assembled a new desktop. as i do not want to reinstall all other programs into my new desktop, i cloned the c drive of old desktop containing windows os and other programs on the ssd of the new desktop. my new desktop is up and running. now i want to buy a license or a product key for my new desktop. so that my both desktops run on genuine windows 11 pro. i am confused how to do it. i do not reinstall windows. i want to just put the product key in the activation window to activate it. i went to microsoft stor

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If I buy Windows 10 Pro box from a store, can that product key be used to upgrade Windows 11 Home to Windows 11 Pro?

If I buy Windows 10 Pro box from a store, can that product key be used to upgrade Windows 11 Home to Windows 11 Pro?

 

Windows 11 Home to Pro upgrade

Want to upgrade 11 Home to 11 Pro. Tried download, but apparently files transferred were for 11 Enterprise. This will not activate; error is "invalid digital license or product key". This is on a new Surface. How to proceed?

Can withdraw/delete this. The suggestion to downgrade - listed below - with a 'fake' windows 10 key works.

 

about buying product key for windows 8.1 pro

i have windows 8.1 pro pre installed in laptop but i want to buy a key , but when i click buy key they show "try after some time " and is not available on windows official website store so how should i buy windows 8.1 pro product key