well but it‘s still unusable funds and „worthless“ tx in a monetary sense. how is this any different than putting a hash into op_return?

Op_return is for child molesters only 😶‍🌫️

why is it worthless and how is it unusable? it pays fees to miners. this is identical to their main service: collecting fees to order things. the person making the timestamp has the private key and can recover some of their funds (again, less the miner fee, as is proper).

It's not worthless. It costs two txs and creates tiny utxos. Hence my note about pure monetary use.