The reason why I'm on a Civ6 Forum right now is because I want to get back into the game as soon as things get better. I pre-ordered this thing! Played 85 hours so far according to my Steam counter. Again, not going back anytime soon because there is no feature in the game I don't have a complaint against. I can always find something wrong even in features I like.
Regarding Civ IV... I have very great expectations.... It's one of these games on my Steam library I haven't opened yet because Civ5 stole 1100 hours of my life.
I'd say, go ahead, give it a try. I personally prefer VI because I love many of the systems in VI, like districts, new roads, dual tech trees etc so much, but there's a reason IV is considered the best game in the series. Another advantage IV has is that playing it is less than a commitment. And I don't mean that games are shorter or less immersive, but that the game is much, much faster than V and VI. In the time you play 30 turns in V or VI, you find out you played 100 turns in IV, simply because you first load up the game within a minute and, when you end your turn, it takes about a second before you can start your next turn. Fair warning though if you've never played IV before, you need more units than in V and VI (one in every city plus a few more for whatever you come across), and
cities can't defend themselves. Early game there are only animals, which can't enter your borders, but when warrior barbarians start appearing, you should have a unit in every city. When attacking a city, it's defended by the units in it, possibly buffed by walls and everything. One more thing I feel I need to mention, some units, wonders etc have multiple tech requirements, and then you need to have all techs. Also, techs can have requirements with arrows and with the picture of the tech required in the top right of the tech. You need all the techs mentioned in the top right, while you need only
one of the techs pointing an arrow to the tech, though having more makes the tech cheaper.