I often used this for many diplo games in the HD version. There’s a hidden trigger that allows you raise population beyond normal, but the only way to do that is by using trigger studio.
But 1000 pop is laggy you may ask? Here’s some tips how to lower lag, remove all life on the map, save few some fish in a scenario. Use Diplofish mod, so each fish has 1 billion food storage, therefore no need to stack fish. Even better modify outposts into monuments and feitorias (without taking pop, or instead giving pop) to give resources and you need to capture them. So you don’t need those laggy villagers ruining your fun.
If not, we may need to find the hidden trigger using something like trigger studio again like many others do for HD. I myself have modded outposts into monuments and feitorias. And made the diplofish mod.