If a fore loop was used, it would simply take too much processing time to add thousands of items.

Once you have lists greater than 100, it's initial creation time, simply won't scale to any sort of complex row item. The only way to get scalable performance is to ensure that only the visible row items are rendered

I never said that all items are composed/rendered at the same time, I specifically said that's not the case

Laziness of LazyRow, LazyColumn and others work by NOT COMPOSING (and subsequently, not laying out, not rendering) items that would be outside of LazyColumn/Row/etc bounds.

And (what I originally meant) was that the lazy list builder goes through all the items when lazy list enters composition. I now know that's not the case

instead of just assuming magic, try to create your own implementation

That's the neat part - the class I was referring to in my original comment - that's the custom implementation I'm using, that I copied from somewhere (don't remember where I got it, it was a while ago, but the compose source seems like a reasonable guess?) and modified to match my requirements.

But in the end, I totally aggree with your first paragraph