There are some regions in some countries with replacement fertility rates.
Countries with very low fertility rates of 1.1 or less will have populations at one third of their current levels in 2100.
Countries with very low fertility rates of 1.6 to 1.8 will have populations at 60-70% of current levels in 2100.
No country has had fertility rates fall below replacement levels and then recovered and increased fertility to above replacement levels.
All of the pro-fertility policies like paying for childcare and lowering the costs to raise a family have about no improvement to about a 20-30% increase. This effect tends to last for a couple of decades at best.