Here you’ve got planet size 16, 3 districts blocked and 5 districts built. So at max you can currently have 16 - 3 - 5 = 8 city districts total. So it shows that you can have up to 8 city districts 4 of which are already used. If you build any of non-city districts you’ll have 4/7 displayed there on the left. If you build a city district it will be 5/8.
I’d argue that unlike Endless Space 2 or other board-game style games where you combine bonuses and get numbers in Paradox games it’s not about precise numbers. There are so many numbers and modifiers that you are supposed to only think about important numbers or very big ones. 16 size planets is better than 10 size planet, no matter what modifiers and blockers it had. One 16 size planet might be slightly better or worse than another 16 size planet due to all of this features and blockers, but you shouldn’t care that much. Just look at the district squares and figure out that one will be about farming and the other about industry.
You are allowed looking and tinkering with all kinds of numbers but you can sort of roleplay, just doing what feels right based on a big picture. Meanwhile Endless Space 2 and similar games just remove the parts they don’t want you to care about.
I prefer ES2 but I can see that it’s limited by AI and balance. As soon as you can reliably beat AI it’s not an interesting game, and in case of ES2 this moment comes pretty quickly. Meanwhile Stellaris AI is even worse but the game is much more about simulation. When it wants you challenged it just throws big bad crisis at you. No one plays to win so even if you know that you’re the winner the game is not solved yet.