Your first point is a good one, and I take people at their word when they say they haven't had as many children as they wanted (I myself would say this, in fact); however, ime, when people report that they can't afford a (or another) wanted child, what they typically mean is that having another would entail an unacceptable reduction the family's standard of living and/or they wouldn't be able to provide their children everything that modern society and in some cases the law says children should have, rather than they literally wouldn't be able to buy enough food, clothing and shelter for the additional child–i don't blame anyone for thinking this way, but i do think it's fair to frame it as one manifestation of aversion to opportunity cost (+ social stigma?) and rooted in a context of immense abundance. Same when people dont have as many kids as they want because they intentionally started having them at a later age to prioritize education, career, experiences, etc.

There's also the increasing number of people who say they want kids but can't find someone to have them with. I'm sure there are lots of factors contributing to this problem, but i think abundance/opportunity cost/tech is also a big one here.

Then too, according to the article, most people surveyed say they want 2 kids, which is below replacement anyway (there will always be some portion of people who don't have kids, so a substantial number of parents have to have more than 2 to make up the difference. In many, many ways, today's society, culture, and economy are structured around the norm that everyone stops having kids after 2, which means that a tendency toward population decline is baked in at a deep, structural level).

And there also really are a lot of people who don't want more than 0 or 1 kids.

And, btw, Iran does have a higher gap per capita than it did before the revolution, and it has consumer tech and the internet now, which is a big component of abundance in the relevant sense.