I agree with the other comments suggesting React. I actually typically recommend just plain HTML and CSS for most projects. But it sounds like you’re building something with a lot of interactivity, so something like React (or Vue or Svelte) is going to make your life a lot easier.

I also agree with other comments that you should postpone worrying about iOS/Android apps for now. Targeting those platforms adds a lot of complexity and will slow you down. So you should avoid them unless your app really only makes sense as a native mobile app.

If down the road you do decide that you want native mobile apps, I recommend using React Native with Expo. Transitioning from React to React Native is relatively easy (from a concepts perspective). But React Native doesn’t use HTML or real CSS (although it’s heavily inspired by it), so you will need to rewrite a lot of your code and change all of your dependencies over to React Native-compatible versions. With React Native, you can have a single code base that targets web, iOS and Android so you don’t need to maintain multiple versions of your code.

If you don’t like React Native for some reason (e.g., it’s made by Meta), you can also look into Flutter which is made by Google.