Yes, it is as you write, I continued to explore the map for expansions.
The solution is simple and straightforward - jump in age. But I won't, because my nature is to explore the limits. I just came across one. If it works, I'll continue, if not, I'll quit the game. The world won't fall apart and I'll have free time. The game constantly takes more time, is unnecessarily complex and requires new hardware - the current technology is slowly no longer enough for me.
I'm in the iron age, map explored to industrial (north america).
Story quest - build a cultural building from the High Middle Ages
Bonus quest - 1/ research the technology that unlocks the cultural building and if i by some miracle skip it there will be 2/ Research Modern Roads.
In other words, impossible for iron age and I reached one limit.