Disgustipated
Deity
In short, no. Forum activity is lets be blunt utterly irrelevant. While some people might think that a handful of very active users uphold the community that is simply not the case. The game is still played moreso then ever.
For a game this old the active player count is incredible. It had a recent peak at over 60.000 players in January! (source https://steamcharts.com/app/289070). This is not even taking the multitude of other storefronts and platforms the game is available on into account.
So no the game is not dead, the franchise is not in the gutter. All that it quite bluntly put is that there is not much news to discuss no real speculation to do, the meta has long since been solved. So what else is there to talk about?
I get that some of the old guard is frustrated but this doom and gloom is uncalled for if you look at the facts. Yes I know that some people do not care about the "casuals" that do not even play on diety but those are the people who by and large buy the game and keep the lights on. The few thousand hardcore fans who sink thousands of hours into it do not account for a lot in terms of sales, so lets be realistic about it.
Edit: What this thread also does not take into account that forums and their culture are slowly but steadily dying. People prefer more immediate communication these days. Discord and other chat software is more and more taking over the gaming space.
You are right that the game is still fairly popular. There are still youtubers putting out civ6 videos. It's doing okay.
As for forum activity, without any new content, it's to be expected. I wouldn't say forum format is going to die out completely. It's just without new activity from the developers, there's not going to be a lot going on. This place gets pretty busy when new expansions or content released. And I admit I'm old school and don't want to see forums go away entirely. It's been something I've done since shortly after the internet became mainstream. I started out on the alpha.owo forums for SMAC. Damn, I've been doing this a long time.