I merged your topics, please don’t create multiple topics about your React .htaccess rules.
Your .htaccess rules look a bit odd to me. The block at the end does some URL rewriting based on the request URL. But I would expect some explicit reference to the index.html file, since that file is the central entrypoint/controller for your web pages.
A quick web search pointed me to this .htaccess example, which looks a lot more likely to work to me: