Check this out. It is an indepth look at the effects the closure of hormuz will have on the world and the terrible timing with the strongest el niño in 150 years at least. There is no oil to make fertilizer, pesticides, or to transport the food.

Heat stress causes plants to need MORE of these things to survive.

We are looking at the beginnings of the worst famine in possibly world history.

Wet bulb temperature is the phrase you are looking for. Above 35 degrees C in the shade above a particular humidity % and your body can’t radiate heat to keep 37 degrees C and starts absorbing it.

If there’s a power outage in that heat, you’ll have a lot of problems.

You might enjoy The Ministry for the Future, by Kim Stanley Robinson. It’s fiction, and written a few years ago, but it begins with heatwaves and crumbling infrastructure in India and you will probably get something out of it.

I mean, probably not. Humans tend to not want to die. So they will stick with these problems for a while, but if people keep dying, the rest will not just sit there and wait to die. They will move somewhere else and figure it out.

The reason why I don’t think there can be a definitive answer to your question is that wealth, infrastructure and healthcare can do a lot to mitigate the issues with deadly heatwaves.
In a region with no AC, no potable water, and no healthcare, society probably wouldn’t survive a week with wet bulb temperatures above 35C for more than 8 hours every day.
So if that happens in an undeveloped region, a lot of people die, but a lot do find some kind of relief that lets them survive. In a developed, industrialized region, like Arizona or Texas, you can have that kind of weather for months, and most people will just hate the heat but otherwise live and work normally. You could picture a hypothetical technically advanced civilization which exists in a climate that is persistently lethal to humans.
Places that face extreme heatwaves need to build countermeasures, but societies tend to be able to do that, even in the global south.

I know this is not answering your question at all. But third world is an outdated term and often considered politically incorrect. I’ve seen imperial core, developing countries, or low-, lower middle-, upper middle- , or high-income countries (depending on the country of course).

That’s what happens when you drown girls and overwork your society.