Hey OP, you should probably get off of YouTube for a bit and go read the Wikipedia articles for those things.

Isochronic literally means "regularly timed" and "monaural" beats are just destructive interference happening before perception instead of after.

Some concepts you should look into:

https://en.wikipedia.org/wiki/Binaural_unmasking - Like binaural beats this relies on two datastreams, one per ear. This is likely the mechanism which makes binaural beats possible, via misuse of the mechanism.

https://en.wikipedia.org/wiki/Psychoacoustics - The brain is fascinating, and does cool stuff with sound. SOME of those things are simple comparisons, some are extrapolation of data from assumed incomplete sets.

https://openstax.org/books/physics/pages/13-3-wave-interaction-superposition-and-interference - Sound is a pressure wave, and as such will behave like a wave in a fluid medium (air is a fluid, albeit very low density)

https://en.wikipedia.org/wiki/Brainwave_entrainment - The "etymology" section reveals why this is pseudoscience. Remember, pseudoscience just means the scientific method wasn't followed, and therefore it can't be respected as science. This doesn't mean its bullshit, or that its wrong, just that the field is tainted because it was not borne of science but of vibes. Literal vibes in this case.

Anyway that's all I have on the subject for now. I looked into the stuff years ago after experimenting with it for so long and not seeing results.

If you read through all of those articles, especially the one on wave interaction, I think you'll figure out for yourself where they're sourcing those 1hz tones and whatnot (hint, they aren't) , and why you may even be able to percieve them despite being far below the range of hearing.