Birth rates are falling in almost every country of the world apart from a few in sub-Saharan Africa. Even in those countries the birth rate is slowing (e.g. where the average birth rate used to be seven or eight children per woman it's now more like five or six).
The world's population is expected to peak by 2100 at the latest, possibly as early as 2050.
Immigration to the west is a short-term solution since immigrants tend to adopt the customs of the host country. So first generation immigrants might have five children but those children will go on to have around two.
As population starts to decline in less economically developed countries, there will be fewer migrants to move to the west. There is also the ethical conundrum of having to hope that other countries stay poor in order to ensure a steady stream of migration to the west (because people only tend to migrate if they perceive there to be better opportunities abroad).
Predicting the future is hard. From an environmental perspective, having fewer humans undoubtedly relieves pressure on the planet. And who knows how AI will transform the job market. I don't necessarily think a falling population level is a bad thing.
However, right now I believe the UK has a fertility rate of 1.5 children per woman - well below the replacement rate of 2.1. Europe is similar. South Korea has the lowest birth rate at 0.8 children per woman, but a lot of countries are following the same trajectory.
This will have a transformative impact on society. I don't think anyone needs to be a supporter of Gilead to recognise that there will be problems (along with some benefits) of an ageing worldwide population.