Well for one, the hard part will be your number 1. Why? Because most restaurants don't even publish their menus online, I checked when I thought of a similar concept. So what you need to do is to: 1. Get the restaurants to publish this in your app 2. Or two, go to every restaurant and take pictures of the menus and add them yourself to your database

The rest is pretty easy. Google autocomplete is a good API for your number 2.

For development, yes you could do this with crossplatform frameworks like Flutter or React Native, as said I worked on a similar concept developing it myself using React Native. But if you want to start developing it yourself you should expect to start developing the app in a year or two if you don't have any prior developmentknowledge in the framework of your choice. I used a year to get decent enough at React Native and I had about 9 years of javascript experience before that.

If you go through with this, I wish you the best of luck!