So yes, the law says there is some unavoidable, unusable waste heat, the question is how much of that heat is really unusable?

For example, you have lava at around 1,000 degrees. You certainly can harvest energy from that, hit some water with it and spin a turbine.

For the most part, once we get under 100C we run out of ideas on how to realistically harvest energy out of it, but there’s still a pretty good delta between that an ambient. The claim of this article is he has an approach to harvest energy at an even lower temperature delta.

If it got to harvesting all of the temperature delta of a system, then we can say “not at all possible based on current understanding of physics”, but if the process leaves some waste heat unharvested, then it’s not yet violating that law. The law just says it gets less and less likely as the amount of heat in question diminishes.