No, the holder/owner of the private key will not sell their private key or give it to someone else.

The ownership transfer will work through a 'transfer signature' that will be signed by the holder/owner of the address.
The message in the signature will contain the address of the new owner, but the new owner won't have the private key of the old owner's address.

Started a new thread
old Bitcoin addresses as 'NFT' on the Bitcoin blockchain
https://bitcointalk.org/index.php?topic=5425241.0

franky1, give it time. Then you will know that it is a 'good' project.