I had a very similar journey. Even after 10 years I sometimes still slip into existential despair, and the remedy is, as you said, a bit subtle: don’t outright

I had a very similar journey. Even after 10 years I sometimes still slip into existential despair, and the remedy is, as you said, a bit subtle: don’t outright ignore it, but also don’t attack it directly. No matter how hard you stare into the void, you will never see anything but darkness. It’s a bit like happiness: if you pursue happiness directly, you will surely fail. Instead, pursue worthy goals and care for others, and happiness will take care of itself. I also learned that, as you wrote, we can lean on human biology. If one asks, “Why should I wish to strive to make progress in life and keep living?” the a suitable answer is simply “Because I’m human and that’s how I’m wired.”