A lot of poor, homeless and disabled people would move to countries with welfare for everybody, like Norway, until they'd get so overpopulated with freeloaders that they have to change their policy. Other popular countries like America would get flooded too, cities would probably get a lot bigger and there'd be a lot more of them. They'd flood to the degree that the downsides of overpopulation would equally offset the original benefits of living there, then equilibrium would set in.

that would mean someone would have to enforce it and thus a single world government - Illuminati confirmed 😵

Skilled labor would immediately leave countries with shitty governments, new influxes of people in war torn regions would move to neighboring countries, cities will become more crowded and expensive to live in.. Honestly not a lot would change. I recently saw a TikTok of girls in the US military being asked why they enlisted, almost all of them were just trying to get away from their poor towns.