The electricity used to mine a block would be the exact same whether NFTs existed or not.

The price of Ethereum is the only thing that drives the electricity costs. Even with 0 txs on the network this would be true.

NFT purchases mean increased eth usage which means eth prices go up and electricity costs go up. But it's not a direct 1:1 relationship. The amount of eth you buy has a much larger impact on eth price.

And if the person you buy the NFT from sells the eth then it actually drives price of eth down.

The fact that eth is moving to Proof of Stake is also massively important. It's a short blip in history where eth isnt running on PoS