What's exchanged on chain is an option agreement. When the option is exercised, the SPV which actually owns the land transfers the title on the national registe

What's exchanged on chain is an option agreement. When the option is exercised, the SPV which actually owns the land transfers the title on the national register. There's a liability framework in place to make sure they do, and stamp duty etc. are paid when the NFT is transferred: that's where the interest is transferred.