What is a realistic pathway to high-income status for most of today’s middle-income and low-income countries? Are they facing an insurmountable climb in a world with declining population and developed economies widening the gap via AI?

To clarify the near future environment I am presenting:

1) Total fertility rate (TFR) has fallen across the board globally without any well defined reason(s). The initiatives taken by the world's governments this past decade to reverse this trend have been almost wholly ineffective. In light of this a declining population over the next few decades (at least) seems baked in as of today.

2) To provide further clarity on the AI inclusion in this question I am not talking about a scenario where AGI, digital god, or whatever you want to call it is created. I am proposing a situation in which AI is developed enough to the point that it can be deployed at a low-moderate cost in the manufacturing and services sectors of already developed economies (USA, China, Japan, etc) resulting in notable productivity gains and possible cost savings.

With my question I am seeking out the optimists' take on how developing countries are going to significantly improve the standard of living for their people over the next 20-30 years in light of this environment.

It seems to me that many of these countries will be in a bleak situation where they are expected to somehow compete (on cost & quality) against already developed economies for an increasingly smaller global pool of customers who will need fewer things and services.

A developed economy like China already smothers many middle-income competitors on both cost and quality in manufacturing with their huge labor force; what happens if manufacturing and service firms in countries like the USA, Japan, Germany, etc. are also able to start doing the same thanks to AI reducing labor costs while still giving productivity gains?

I understand the world economy is not zero sum but it still seems to me that for today's still heavily agrarian or otherwise underdeveloped economies there is an increasingly narrow path to becoming a global player in the manufacturing or (non-tourist oriented) services sectors.