This should probably go into the stats thread but:
1m+ sold copies is a solid but not great base. And if I look at the gamalytic numbers, which says 1m copies and average concurrent players since release are 7.2k. Hence, the rate of active players of 0.72% isn't bad.
CK3 sits at 0.38%
Civ VI sits at 0.36%
EUIV sits at 0.28%
AoE2 DE sits at 0.20%
Stellaris sits at 0.15 %
Civ V sits at 0.10%
Old World sits at 0.10%
Humankind sits at 0.04%
Beyond Earth sits at 0.02%
Now, of course this isn't in any way clean, as the games were released so long ago, and civ 7 just recently.
But if we look at undoubtedly successful games that were released in the same time frame as civ 7:
KCD2 sits at 0.41%
Expedition 33 sits at 0.40%
Monster Hunter Wilds sits at 0.39%
Again, this is not really clean, because these game likely have a way larger console audience. Yet, I don't see why console players should play the games they own more or less often than steam owners. I know that long-term, the different genres will make a difference for retention, but so far, I'm actually surprised to see them that low.
So, it seems that the game is played by its owners to a satisfying degree. It just doesn't have that many owners yet. In other words: at some point, FXS need to find more owners to keep up the support, and not necessarily improve the game for the people that are already owning it and play it

. These owners and players can probably be seduced to buy DLCs with shiny things if marketing is clever, as it was the case for civ VI as well. The first larger discount (just now) increased the player base, but then again, not by that much.