You can blame the jews, feminism, or whatever. But if you look at any non-white country that's achieved capitalism and industrialization, the birthrates are tanking there as well. Initially, birthrates spike up thanks to modern medicine preventing infant mortality, as the country develops industrially, they start going down to "western levels" of <2 TFR.
This is true for all western countries. You can look up the birthrates of any western(ized) country and see a fertility spike with the introduction of modern medicine, then a continuous drop in TFR as the country becomes more industrialized.
The ugly truth is that in an industrialized, capitalist society, you're not required to breed. Whereas in any pre-industrial society, having kids was a necessity. More sons meant more farmhands meant more resources, especially as you neared old age. With infant mortality, there was no guarantee the child would survive past 3, so it was better to keep breeding.
Breeding was an environmental necessity, not a biological one. There wasn't a gene telling farmers to make 6-10 babies: The environment "forced" them to do that to survive.
With contraceptives and without an environmental or genetic compulsion, people usually make children at a TFR of 1 or 2 and are done.
Despite being industrialized societies, both Nazi Germany and Israel managed to raise birthrates through government programs somewhat successfully. But I think that's useless when you consider what's coming.
Most people might lack the genes to have 12 children per couple, but there might be some that do. Their population will grow naturally, and thanks to their huge numbers, they will spread their superbreeder genetics to the majority of the population. Those who have an average of 1-2 children per couple will be bred out, or mix with the superbreeders.
Meaning, if Karlin's superbreeder theory is correct, in a century people will be complaining about the opposite.
Religiosity correlates with high birthrates. So it's fair to assume that superbreeders will appear from radically religious communities. The Amish, Mormons, Orthodox Priesthood, Haredi Jews and generally "traditionalist Christians" all have a high birthrate. And are all likely candidates for this genetic transformation. In a sense, the meek will inherit the earth.
You shouldn't base your understanding of Christians on internet people. Especially internet people on imageboards or in the "right wing" internet sphere. On average, they are somehow psychologically damaged or suffer from a mental disorder like autism or homosexuality. Their overrepresentation conjures the false impression that finding a girl to have children with is an unsurmountable task that requires giving up everything that made you happy. If you're on these kind of social fringes, it is hard. But the "normalfag" non-liberal Christian has no trouble finding a partner to have several children with and be happy in the process.
On a personal level, you don't have to do anything. "Be fruitful and multiply" isn't a conditioned commandment, you follow it regardless if the population is booming or shrinking. Celibacy is also biblically supported, as long as it's a celibacy focused on God. As a Christian, all things should be.