Right now for Political Structures we have various government types in both Civ VI and Humankind, with various features, pluses and minuses to them, but no real difference in their structure and development. From what I have seen so far, this is true of both Humankind in its currently-revealed state of development and of Civ VI.
More importantly, there is no difference in the structure of the Civ that has any form of government: the very real differences between a pastoral group, even one as large and influential as the Mongols, Lakotah or Huns in their respective realms, or a City State political structure like the Classical Greeks or Gauls.
Given that the games have delved deeply into differences in architecture, religion, language, and culture from all parts of the world (with, admittedly, mixed results which give the CivFanatics hundreds of topics for discussion) it is becoming embarrassing that they cannot model variations in Political and Social Structure represented by the pastoral and city state periods of Civ development AT ALL.
Civ VI swiped at the pastoral civ with the Maori - a 'nautical nomad' starting Civ, but it basically progresses only fitfully until they settle down and found a city. Humankind's 'neolithic start' looked like a framework for a 'nomadic/pastoral' start and game style, but it apparently amounts to little more than an extended First Turn in which you get to beat up some animals and find a good city site. There is no real indication from either that 'nomads/pastoralists' could have any scientific development capability, which would come as a mighty shock to the Gauls, who managed to develop the long iron sword, link mail armor, sophisticated saddles and riding tack and chariots, wagons, and well-paved and surveyed roads over which to ride in them, mostly before they had founded any cities!