It's about both. Women are now indoctrinated to "wait until career is solid", i.e. their 30s.
For some ethnic groups, that's the age when they can't have children. For others, it's age where they have severe problems having children.
Biologically, women are primed to start having children in early to mid teens (easiest birth in terms of complications, but low viability of fetus and baby size making it suboptimal). Optimal window is where ease of birth is going down, but still very high up, while viability of fetus and baby size converge on optimal. That's between 16 and 22 (depending on ethnic group). Everything past that is reduction in all three, and the curve's downward trajectory rapidly accelerates when geriatric pregnancy stage starts, ending at zero marker (sterility).
Women are the carriers of culture, meaning they enforce the norms. That's their biological role in our species. So when the norm is "do not have children until you have a solid career, be a boss babe so you can provide best possible life for your children", they prioritize career and shame women who don't. And then when they finally get set in life, they try to have a child.
Find out that they're not getting pregnant. Get to a doctor. Get tested. Find out they're well into geriatric pregnancy range. Get scared, harvest eggs (far too late, you want to harvest eggs when you're in your early 20s at the latest if fertility is your goal, and even then success rate is not great). Do the first round of IVF. Nothing. Second. Nothing. Go to the doctor again, and get reminded that deep into geriatric pregnancy means that even with IVF, chances are low.
Get desperate, depressed, often borderline suicidal. "I've lived my life the way all other women told me I'm supposed to live it, and now I find out that it was all a lie, a weapon they deployed against me to prevent me from having children so theirs don't have to compete with mine?"
That realization is for top 20%. The rest just get depressed and don't understand why reality doesn't bend to their socialization. That's the stereotypical millenial woman in her late 30s and early 40s, doing all the drugs and all the alcohol and all the SSRIs to just drown away her misery, and then complain on tiktok about everything.
But a lot of women can still have that one child with IVF, as long as they start in their thirties, and they're not of african descent.