Here's the AI summary:

Which is consistent with what I was able to glean from his argument by reading the introduction. It's of course not fair to think his argument is accurately summarized in the introduction - it's just an overview. But from the beginning, it seems his claim that the modern nation-state is imaginary is based on the premise that every community that's larger than a small village is imaginary:

In fact, all communities larger than primordial villages of face-to-face contact (and perhaps even
these) are imagined. Communities are to be distinguished, not by their falsity/genuineness, but by the style in which they are imagined.

I mean....yes? Obviously? If start from definition of a non-imaginary community requires that all of the members be engaged in face-to-face contact for it to be real, then of course something like a nation (or nationalism in general) has to be imaginary?

But I don't think many people would ever accept that starting principle as true, from a cultural or sociological or even a political point of view. No communities exist higher than Dunbar's number? I mean, obviously that would mean that the Black community is imaginary, the Jewish community is imaginary, the gay community is imaginary, the chess community is imaginary - not just world-wide, but in the U.S. or even a single state. There is no gay community in New York state. There is no gay community in New York City. There is no theater community in New York, no community of Shavians in England, no community of Miami-Dade County environmentalists.

So there's no such thing as a community of Slovaks. There's no such thing as a community of Armenians. Or of of Thai. Even though the tribe known as "Danes" formed as a distinct cultural grouping more than a thousand years before the formation of the modern nation state, and established self-governance for themselves over a defined geographic area, forming their own language and traditions and cultural observances common to themselves and distinct from their neighbors....the "Danes" are an imaginary community. Always have been, for as long as they were more than a village in number. They were imaginary in 900 AD, and imaginary in 1400 AD, and so they were obviously imaginary in 1648 AD. So clearly "Denmark" as a community has to be imaginary as well.

I suppose that's all well and good if you want to build a theoretical critique of modern nationalism, and I look forward to reading the book. But I don't think that is has any utility for guiding what people should or should not do in the real world. I don't think that many people - or even more than a primordial village's worth of people - would accept the proposition that all communities larger than a few score are imaginary for any practical purpose.