Originally the discussion is about people "using Bitcoin to pay for their McDonalds". Then the commenter erroneously stated, in response to that, that a "bitcoin transaction uses the energy equivalent the entire lifespan of a tree". El Salvador is using the lightning network. These transactions are done off-chain. So the transaction fees do not even go to miners. There can be thousands of McDonalds transactions that occur off-chain and are eventually settled on-chain in one transaction. Processing and validating transactions is very computationally easy. You can indeed do it on a laptop.
Mining blocks is a separate issue. If you ignore the competitive security race, then the network can indeed function on a laptop. Most the mining race that is currently occurring is because people are fighting to win the block reward - this would happen even if nobody were transacting, and someone doing a lightning network transaction has truly negligible effect on that energy usage.
When you said "bitcoin would become valueless, as everyone with a laptop could produce their own longest blockchain where they have half of all bitcoin" this shows you don't understand the process, because the difficulty would rise until people can no longer produce blocks so rapidly. You're describing a situation where miners are not even on the same network so it doesnt make sense