Human population and the loss of "purpose"

For the last 10,000 years human population has grown from a few million to now over 8 billion. Let's stipulate that this success added meaning to many humans lives both on an individual family level as they struggled to have lots of kids and on a societal level as new technology enabled larger numbers of humans.

Now, for as far as I know, the first time, humans are globally choosing smaller families or no children at all. Plus new technologies no longer represent a leap forward in enabling "meaningful" population growth. Here meaningful population growth in the sense that it helps human survival or allows us to reap the benefits of more diversity.

So for instance clean energy might enable us to safely get past 8 billion but 8 billion was already "enough". Technology that further automates work or allows a longer or healthier life span are also outside the 10,000 year drive for a larger human society.

So it seems human beings have lost the biological drive. If we add the loss of this biological drive to the equation what philosopher(s) best addresses the current human condition post accomplishing 8 billion?

Changes in worldviews and scientific progress are indeed part of the topic related to the philosophy of technology; philosophers of science and technology have and do write about these topics, drawing from various philosophers and their works. The transformation from hunter-gather to spacefarer has a certain fascinating element. Despite the inequalities of health and wealth in the world, we are now capable of growing, housing, and providing energy for everyone on the planet. Germany, for instances, has to deal with negative energy prices (bloomberg.com) demonstrating the potential for surplus even in scarcity economy. You ask:

Has human "victory" bereft us of purpose and what philosophers have written about this?

An early great critic and thinker about the effects of technology around the time of the Industrial Revolution who should jump to your mind is that of Karl Marx (SEP). Adam Smith had a particular vision of what a free market was, but Karl Marx with the benefit of hindsight was able to see how capitalism and markets actually materialized. He was very critical in how the capital class was able to use economics to take advantage of others, and laissez-faire capitalism is known for a number of abuses. Yuval Noah Hurari cites fractional lending, for instance, as instrumental to European military dominance.

Slightly later was Friedrich Nietzsche. Here we find a real swing into modern philosophical themes of power, purpose, and meaning. From WP:

Nietzsche's work spans philosophical polemics, poetry, cultural criticism, and fiction while displaying a fondness for aphorism and irony. Prominent elements of his philosophy include his radical critique of truth in favour of perspectivism; a genealogical critique of religion and Christian morality and a related theory of master–slave morality; the aesthetic affirmation of life in response to both the "death of God" and the profound crisis of nihilism; the notion of Apollonian and Dionysian forces; and a characterisation of the human subject as the expression of competing wills, collectively understood as the will to power. He also developed influential concepts such as the Übermensch and his doctrine of eternal return. In his later work, he became increasingly preoccupied with the creative powers of the individual to overcome cultural and moral mores in pursuit of new values and aesthetic health.

Another philosopher who has written about the modern world and personal meaning is Jean Paul Sartre who is perhaps one of the most famous existentialists. Existentialism as a philosophy insists that there is No Great Chain of Being, and that in a secular world, people have to take responsibility for deciding who they are and what they do. In Christian Europe, one had a role and a relationship with the Church and God that was essentially assigned to them at birth. But after the Renaissance, and the emergence of modernism, people increasingly had to determine this for themselves. Søren Kierkegaard had raised these sorts of issues a century earlier, but the two great World Wars raised the specter of global warfare and nuclear annihilation heightening self-reflection about life, death, and the evils of technology.

Friend of Sartre and fellow Frenchman, Albert Camus took existentialism to an extreme (he insists out of it entirely) and wrote about a philosophy called absurdism, where meaning was not even possible. His most famous work on the matter is probably The Myth of Sisyphus which explores in florid essay form the nature of literal and philosophical suicide. While aiding the French resistance in Vichy France, Camus was witness to the Nazi war machine and eventually the Holocaust. His work reflects the same sort of existential dread that Viktor Frankl, a survivor of the concentration camps himself, contemplates in his book Man's Search for Meaning. From WP:

Man's Search for Meaning is a 1946 book by Viktor Frankl chronicling his experiences as a prisoner in Nazi concentration camps during World War II, and describing his psychotherapeutic method, which involved identifying a purpose to each person's life through one of three ways: the completion of tasks, caring for another person, or finding meaning by facing suffering with dignity.

It's difficult to read great philosophers like Marx, Nietzsche, Sartre, and Camus and not get an idea that since the Industrial Revolution and the advent of capitalism, human existence seems fundamentally different than during the Antiquity, the Dark Ages, Medieval Europe, and even the Renaissance. These writers themes are often atheist, and deal in critical examination of power. And are related to an entire philosophical movement in Europe called Critical Theory which seeks to tackle and ameliorate imbalances of power and wealth largely in the absence of any idea of a Creator or Divine Plan that had remained popular even into the Enlightenment.

I don't think that "human beings have lost the biological drive", I think they have gained the ability to do other things. Just a few generations ago (in the parts of the world I know something about) women could not own property, vote, work outside the home, or lawfully refuse to be impregnated by their husbands. What exactly could they have done otherwise? Lots of folks have written philosophical works about this topic, so it is easily findable.

I have read about why fertility has fallen below the 'replacement' level (2.1 children per woman on average) in many countries, and the reasons vary. In some it is the economic situation, in others a lack of support for childcare and other needs for working women. In one place (Japan) it sounds like the young men are not "growing up" to be anyone that a woman would want to marry, let alone have children with.

Materially, things have gotten dramatically easier with explosions of options in many areas, just in my lifetime. I grew up spending summers in a cabin on an island where there was no heating, A/C, running water, roads, mail delivery, no TV, or telephone or even a radio. Options were basically swim and hike in the daytime (boiling water to hand wash dishes after every meal), and read or look at the stars at night. I often feel that most people could have benefitted from that upbringing.

What I see is that making things materially easier deprives people of opportunities to learn and develop themselves. Increasing options leads to paralysis and "loss of meaning". Existentialism talks about that, but I never saw it propose any solutions so I think it is rubbish. My solution is: read more books, get your hands dirty repairing things, and learn to be utterly skeptical and think for yourself. Then there is no end of meaningfulness and purpose.