Due to Carnot's law, you can't get much electricity that way without a big temperature difference. Think about it: the AI machine would have to run at at least 100 degrees Celsius to boil the water, and that's the bare minimum.
But if we can make computers that run at, say, 2000 degrees, without using several times more electricity, then we can capture their waste heat and turn a big portion of it back into electricity to re-feed the computers. It doesn't violate thermodynamics, it's just an alternative possibility to make more computers that use less electricity overall (an alternative to directly trying to reduce the energy usage of silicon logic gates) as long as we're still well above Landauer's limit.
But if we can make computers that run at, say, 2000 degrees, without using several times more electricity, then we can capture their waste heat and turn a big portion of it back into electricity to re-feed the computers. It doesn't violate thermodynamics, it's just an alternative possibility to make more computers that use less electricity overall (an alternative to directly trying to reduce the energy usage of silicon logic gates) as long as we're still well above Landauer's limit.