At the risk of being stereotypical, I'm playing Workers and Resources: Soviet Republic. I just recently finished setting up oil industry and rail for exporting fuel, alcohol, and food. The alcohol is only for export and no-one is addicted. I'm determined to achieve self-sufficiency and am working on the steel industry next!
I've also reinstalled Morrowind with a monstrous Vanilla-Extended Mod Pack from the Open Morrowind Modding community and spent last night sleepily clicking my way through 440 mod downloads. I've succeeded, and am now slightly terrified of the monster I've created.
It's definitely both very complex, with layered mechanics, and also honestly things aren't always well explained in game. I have a lot of time in it and I still run into new systems that I can't get to work without looking through answers from other players and guides etc. I find it rewarding now that I can make sense of it and understand a lot of the core systems, but it took a while to get there and I also didn't play the game for a long time after buying it because trying to build something for the first time is like hitting a brick wall.
But, if you're interested in more accessible city builders, I can recommend a couple - try out frostpunk, the original one, great vibes and music and it's generally much easier to pick it up while still having lots of room to optimize.
For something completely different, Per Aspera let's you terraform mars as an AI and make narrative choices while building huge systems of industry and extraction across the whole planet. Very satisfying although be warned that it's impossible to make nice and neat cities because of the way its road building and placement works.