CPUs do no thermodynamic work. They do computational work, which does not count as work in work-heat-energy balance. All electrical energy consumed by CPU turns into increased internal energy of the surroundings, which is, in short, called heat.

Not all of the electrical energy consumed by the CPU is used by the CPU for computational work. Some of the electrical energy transfers out of the CPU to other components. The TDP of the CPU is not concerned with those other components. TDP is not a useful measurement of the amount of electrical energy a CPU can consume.

All consumed energy is used to produce heat, by definition of "consumption". If some electrical energy transfers out of CPU to other components (this is indeed possible), then by definition this energy is not consumed by the CPU. The meaning of TDP is explained in the article - Intel's value of TDP was such a measure, but is no longer so.

All output power is thermal though. This is basic thermodynamics. A negligible amount of input power will be distributed outside of the CPU die which will be dissipated as heat a short distance away. Pray tell, what other energy form do you think this input is becoming anyway?

I imagine some tiny percentage would instead be dissipated as light/radio waves or sound too - hence my ~99% comment.

There's also this: (https://en.wikipedia.org/wiki/Landauer%27s_principle) if you want some light reading.

Indeed there will be some piezoelectric effect and some EM emissions on the order of micro watts compared to the 10s of watts burned by the CPU. But the poster I was replying to seemed quite confused about the fate of power in a CPU used for computation: It’s dissipated as heat.

Well some power is used to run the fans which ends up partly turning into kinetic energy of air leaving the case. Sure, that may also manifest itself as heat somewhere down the line, but not in a way that is relevant for this discussion (and indeed you have to draw the line somewhere).

It's probably fairly neglible though, probables less than a watt in most systems.

The fans aren't the CPU.

Oops, you are right.

In a CPU ~99% of it should be, how else is the power dissipated?

Where else would it be going to? The RGB LEDs?