Another thing is tune whistling/singing, when you think about it it is even more basic then language, just "predicting" the next note in a sequence of notes one already has stored in memory, so pointless, yet objectively satisfying for some reason. I often sing/whistle in the background, I've found it only reduces my ability to think when it gets in the way of what I perceive to be low value work, I think this is due to it being a very low energy, low value activity, whereas similarly low value work may be higher energy, and so it becomes unbearable to stay focused on the work without reverting to a lower energy activity, rather then the internal music overcoming the work. As I acquire further high value work, and surround myself with people who would rather not hear whistling/singing, this habit has decreased considerably. It may be the case that such internal monologues or LLM like activities are not as low energy straight thinking, but maybe they serve some kind of "idling" purpose, reinforcing pattern/logic/computation/memory pathways in the brain, for cheap.

Out of curiosity, have you ever been kept up awake at night by your thoughts, either before an important event or after some problem? If yes, and you have no internal monologue, how does this manifest? Do you simply not feel tired? Or do you feel tired but unable to sleep? Or otherwise?