It looks like you are using Vite to compile and bundle your react project. I don’t have a ton of experience with Vite, but I will try to help… React needs a div element to hook into so that it can inject the react app into the DOM.
I’m assuming your vite project has some sort of index.html file? This is how you app actually gets into the DOM and onto the page.
You need to make sure that your app-block snippet (.liquid file) acts as this index.html. This is where the javascript source is loaded from and you need to set up the proper structure for react to inject itself into.
If you share some of your project setup, I can try to help more.