With regards the question of whether a) the world, b) one's own country is overpopulating or failing to reproduce sufficiently to work and do essential jobs in the future, the answer is both. In many under developed communities there is overpopulation- but you can't say that an overpopulated village in Africa means England - or Wales- will be bursting at the seams. They're not able to teleport here! Sadly in many underdeveloped communities where the birth rate is very high, many children will die before the age of 5, many mothers will die in childbirth and many men will die in unsafe workplace conditions.
At the same time, there are many first world nations with a greying population and a declining birth rate - the list varies from year to year but in the last 10 years, nations like Italy, Japan, South Korea, Germany, France, Estonia have been on the list. But it does change, for various reasons. And if they do take in people born and raised abroad for work or who settle for other reasons (eg fleeing war or economic deprivation) and start families, then the figures improve again. All developed nations have always found solutions to increase their birth rate or workforce population if it drops too much, whether that is financial incentives to have children, encouraging migration and temporary workers from abroad, or both.
No nation is currently on its knees as a result of having too few births. Countries that have overpopulation and very high birth rates - historically this has always been shown that if the educational attainment of girls and women improves then the childbirth rate slows down and infant mortality and maternal mortality often improve also. (It doesn't mean making them get A grades but instead it means keeping them in education for longer till at least 16, even better, till 18, because previously they were often not sent to school or if they were, they used to be prematurely removed by parents from school before the age of 14 or even as young as 10).