@thetatautau ads in general can be unpredictable as to how much money they make. There are lots of factors that play in and Apple made it even more complicated by limiting developer's access to unique advertising identifiers. Subscription models are the best for apps, the 1-click pay options have made users significantly more likely to pay for apps. For this game, you'd probably have like 50 free levels and then users have a way to unlock more, but make it difficult. And then also sell your levels by the 50 or 100 pack for like a dollar. 1 dollar is somewhere around 1000 ad impressions, so definitely good to have a pay option. But with level packs, you can still have ads and maybe make ad-free be a yearly subscription, separate from buying levels.
Your game is also simple enough that it can be updated without app store updates. Your puzzles could be added and stored to a cloud database, and the new puzzles could be instantly available to the user. So you could easily build up a huge number of puzzles and maybe eventually charge a higher price to buy the level packs in bulk.
I may have poorly worded what I said, I've made apps for businesses and put them on the App Store and Play Store. They weren't games, not much fun to develop. But I learned a lot about cloud services and backend infrastructure making those apps. I need to follow my own advice above and get something out there and start making money. Working for businesses drained me, and I've just recently decided to pursue game development and be a teacher. Don't wanna sell my soul anymore and maybe I can inspire some kids to get into game/software development. Also gotta have a backup plan lol.