I'm playing version 3.0.4 and a screenshot from it. I don't know if there were any changes.
Religious buildings give me +10% food. There is also a monopoly on olives, which provides another 10% of the food. Each city has frequent WLTKDs, which adds up to another 15% (I might be confusing) population growth. There is a food caravan going to every city in my empire, except Yekaterinburg.
The spread of religion by missionaries provides food for the capital. I often complete CSs quests about trade caravans.
Hanoi receives 1 caravan, Yekaterinburg is far away on the island and independently obtains food. Without the caravan, Hanoi would be smaller than Yekaterinburg.
31+29+26+27+30+22+25=190 citizens, without a captured and burned city, which gives +163 supply. Tech level -159.
By comparison, CSs have between 15 and 18 citizens.
Japan has 32 citizens in the coastal city, which is more than my capital. Although my empire has many food bonuses.
If we reduce food bonuses and population growth bonuses, I would expect around 17 citizens without caravans and up to 23 citizens with caravans in non-capital cities.
23*7=161
161/190=0.8473 , the population would be almost 15% smaller.
0.8473*163=138.1099 would be supply from the number of citizens
163-138=25 this is how many units are obtained from the excess population.
The unit limit would not be 71, but 46.
Perhaps the decrease of unit supply would not be so dramatic. The formula is unknown to me. But the effect must appear.