OK, I'll bite.
How long will it take until humanity is extinct based on the global birth rate of [checks notes] 2.51 children per woman[0]? Please show your working.
When you say "developed countries", I assume you mean the G20 with a birth rate of 1.65 births per woman, but that includes the most populous nations on Earth (China and India).
That means what people are actually talking about is "the birth rate is fine, but it's rich people who will soon be outnumbered". That's not a human extinction event - that's a call to action on equality and inclusion, and to ensure wealth is more evenly distributed.
A lot of people who make these extraordinary claims of extinction risk are themselves very rich (Musk) or people who adulate them (people on Twitter). By insisting birth rate in the G20 is the issue that needs addressing, rather than wealth inequality, they make their motivation pretty plain to see.
But none of this prices in climate change as a risk. Is a human extinction event (or tipping point event) going to happen sooner or later than an extinction event caused by climate change?
As the population decreases and human consumption of resources decreases, will climate change accelerate or decelerate?
Why is birth rate a problem for people of this generation to address urgently, as a higher priority than climate change?
If it is a priority that requires direct intervention, why should that action be - as per the person I was replying to originally - require women to have less choice and autonomy? What method will this take? What other choices are there?
Frankly, I don't know why I'm putting this much effort into arguing with a flawed "philosophy" straight out of the Andrew Tate handbook, that doesn't get backed up by numbers.
If you're scared of poor people having more children, do something about poverty, not telling women they should have a moral obligation to stay at home and bring up your children.
[0] https://www.theglobaleconomy.com/rankings/Fertility_rate/