While it may not have the shine and polish of Sid Meier’s Civilization 6, at least FreeCiv doesn’t force glitchy unwanted advertise-- er, launcher updates that break the game years after release:

https://www.reddit.com/r/civ/comments/nkdh4d/follow_up_to_th...

Truly can’t describe how aggravating it is to have Civ 6, my after-work happy place, effectively torn from my hands years after purchase by some MBA manager and bargain-bin programmer. Bypassing the launcher only sort-of works on my PC. Can’t roll back to an earlier version because Steam. At least we’ll always have FreeCiv.

I still stick with Civ 5 myself. Never really cared for Civ 6.

Although Civ isn't really my type of strategy game anyway. It's fun, but man the games take forever(and I play classical chess...). And for single player, the AI is so dumb, annoying and belligerent it kinda saps the fun out of it for me. The difficulty levels in Civ 5 are actually all the same dumb AI, just with varying levels of cheats enabled. I believe on Diety it starts with 3 settlers or something bonkers like that, and a huge production multiplier to boot. And yet the AI is still so dumb that a strong human player can win a game against 5 diety AIs on the same team. If Civ 5 had a somewhat passable AI I would play a lot more I think, because then I could actually get practice put of single player mode.

Additionally there's so much busy work(micromanaging tiles/workers can get pretty tedious). I feel like strategically and tactically the game is pretty simple. In games against much more experienced players where I get a lucky start and we're even entering the endgame I tend to win because I'm just a better tactician due to studying chess. But they usually get much better early games because they know all the mechanics more intricately, which is basically rote. I'm kind of more partial to Risk for that reason. The rules are dead simple, yet it is still tactically very complicated.

If you're interested in F/OSS Civ 5, there's a decent F/OSS mobile-first implementation called Unciv.

https://github.com/yairm210/Unciv

I've played a terrifying number of hours of it in bed on my phone.

edit: on AI, since I'm rate-limited:|

I think it gives higher AI difficulties a massive productivity boost so they just crush you under a flood of units.