Well no. That’s a wildly incorrect take.

Birth rates are already decreasing and are below replacement rate in many places already. Fertility rates are at an all time low. They naturally decrease as income and quality of life increases.

The global fertility rate is 2.2 births per woman. Which is just barely above replacement. In most developed nations, that rate is down in the 1.6 range, well below replacement.

Total Human population is excepted to peak within 50 years and then begun naturally declining, but many countries are already there. China has seen several consecutive years of population decline. India is seeing a leveling off of population growth and will soon decline. The US is increasing solely off of immigration. Japan has a decreasing population. Same with Korea. 8 EU countries have seen population declines over the last 20 years.

If you wanted to see population decline in the US specifically, banning immigration would do it and we’d see a decline in the next census.