37 with Kongo. Around turn 280, couldn't finish the game unfortunately, ran into the bug where the game keeps crashing on next turn.
I think Kongo is the best Civ for going tall in this game. Mbanzas allow you to keep growing nonstop, without hitting the usual housing breaks. Extra passive food from it as well as Relics is great too.
I stayed on 6 cities that game, 4 of them hit 30+ pop, and was getting a ton of science & culture just through passive population gains alone. With that many citizens all the district are being worked too, so you get additional science and culture from that.
Just have to make sure you stack Zoo & Stadiums as much as possible, amenities are very hard to keep up without overlap bonuses.