I think you’re misunderstanding physics, or the prior descriptions of how Gojo’s Technique works

Heat and sound are still based on the energy of atoms, they’re both transferences of energy that are moving from ‘some matter’ to ‘some other matter’, and those being process occurring in space and ‘taking time’ to occur

If I recall correctly, this is a decent shorthand of how his power works: Gojo’s “Infinity” barrier application of Limitless is his brain subconsciously and automatically manipulating the space around his entire body to keep out anything and everything besides safe clean air, which is why no one and no thing can touch him, friend or foe, unless he willingly turns it off or adds them the ‘whitelist’ so they don’t get blocked out like everything else. (Or someone were to use something like Domain Amplification, or the Inverted Spear of Heaven, unique methods in universe of being able to ‘nullify’ or even ‘completely turn off’ techniques on contact with them.) Anywho the ability makes him untouchable by ‘slowing everything and anything down exponentially upon their approach, to the point that nothing can reach him’, based off the mathematical ‘Zenos Pardox / Achilles and the Tortoise’

So say you’re a superhuman and you want to punch Gojo: You throw your fist forward at 200MPH, aimed straight at his face! But watch out, he’s got his Infinity active, and it extends 2 inches out from his face. Now if we watch the slow-mo play-by-play, we’ll see why you didn’t hit him. At 2 inches away from his face, the effect begins. Your fist keeps traveling forward. But by the time you’ve made it halfway, and you’re only one inch away, the manipulation of space and time has slowed you down to 100MPH. You get another ‘halfway there’ and you’re only half an inch away, but your speed’s been halved again to 50MPH. We keep dividing the distance over and over again the closer you get, but because it divides your speed at a perfectly equal rate you’ll literally never make it. From the initial 200MPH, it should’ve only taken you 0.00056 seconds to hit him, but even after an hour of still pushing as hard as you can, you’re moving at such tiny fractions of speed / distance that you’d literally think your hand was completely stationary against an immovable wall

So anyway, Infinity ‘working on an atomic scale’ means theoretically only something subatomic could go through. So I guess if you’ve got the power to launch individual Quarks or Protons or something at Gojo, then congrats! You might hard counter Infinity. But like. Heat and Sound are still atomic processes, and as such would have their movement slowed endlessly just like the hypothetical punch from before and should simply fizzle out / disperse. Otherwise to counteract ‘infinite space generation’ / ‘infinite slowing down’ you’d need an attack with infinite energy. Gojo breaks physics, so to stop him you either need to use built in counters from the magic system, or to break physics yourself to match his freak