1. Some demographers say that for the first time in recorded history the total fertility rate of the world will be just under replacement this year (2022 TFR=2.24, world replacement level being 2.23, as opposed to ~2.1 for first world countries).
2. Middle income countries are en-masse entering a stage of low fertility, a phenomenon that 50 years ago was only observed in few high-income countries. Even some poor countries have a rapidly declining fertility with few of them under replacement, and a bit more poor countries are expected to join this under-replacement stage. This means that immigration as we know it will change in demographics and magnitude, since the source countries will have their own problems as well.
3. Aging developed countries will perhaps have to change their approach to immigration: Canada is the poster child on what not to do and is being observed by several researchers around the world to have a glimpse of what's to come. A vicious cycle is born: Their native youth has not a broad margin by which to start families, so to compensate they take in high levels of immigrants relative to their population (Century initiative, as called by their government), little jobs or housing is added (for a variety of reasons, not all of them political) and home prices go up while wages in several professions are depressed, back to square one. This is particularly pernicious in Canada given their welfare system for elderly citizens, their immigrants aren't having enough children to compensate and in some regions their TFR is actually lower than that of the native population. The bane of a generous pension system is an inverted population pyramid, this is only exacerbating the problem. To ensure non-collapse either migrants have to put a lot more than they give or they take increasingly more immigration. It seems Canada already choose, and has a window of a couple decades given what I just said in point 2.
4. How will other developed countries react? Will they become high-tax gerontocracies like future Italy where the youth has to escape from for professional and entreprenurial aspirations? Or will they battle for high-quality immigration instead and make their economies more competitive and dynamic? Will they rely on their diaspora in Latin-America to compensate (such as german, spanish, japanese, croatian, italian, portuguese) like Spain and Italy are already doing, in the style of a great recalling? Will they, like Canada, start recalling mennonite communities from Mexico? In the US, will the amish carry the bulk of births in rural counties and Hasidic jews offset the birth crisis in urban areas (they both have a falling TFR, but still greatly above replacement)? Israel's TFR is solid and their population pyramid is actually a pyramid, do we look at them on what to do? Many african cities are on the brink of having sub-replacement TFR, will they have internal migration within the same continent instead of external movements?