[....]I'm not a programmer, but why not try Polygon, for example.
OP already tried Polygon as he mentioned in his previous comment.
The reason I choose to build it on Ethereum is that I tried before with another game built on Polygon which is a well-known blockchain, but in reality, people don't really use it, and the hype is about promoting Polygon, not the projects built on it, and this is why the project died even before started.
Understandable but how certain are you that Polygon was the problem? It's true that it has less users compared to Ethereum so there is still the need to promote the chain first over the projects built on it but have you done enough for the game? I mean maybe the concept was different than what you're trying to build now. try to consider this again.
Why do I choose to build it on blockchain in the first place?
The game challenge is time and time can be bought from the game, a pay-to-win concept that helps new users to keep up with the first comers, otherwise, it won't be fun to wait to get invaded every minute by users who started before you.
The good thing about these games is the time because in order to keep your town prospering all you need is a few minutes per day to collect resources and upgrade buildings or create new ones, so technically it's one transaction per day that handle all the updates for you. So you are playing by not wasting your time playing

The fun part is when you start trading resources and shares in the marketplace, it's about predicting other users' productivity, promoting your own town, trading countries' bonds, and of course, getting your town up in the leaderboard.
The game works without the blockchain, but when the money is real, it makes it more fun because the steps you take are well calculated and the town gives you more status than holding a rare NFT or something similar in the crypto space.
The idea sounds good. I hope you get a good backing for this project.