[Tetra](https://www.tetraframework.com/) might be an alternative if you’re hell-bent on not using React.
But, if you want to ship quick, have a maintainable codebase in a technology a lot of devs are familiar with and have the power to instantly ship for mobile (and buy yourself some time to build one in React Native; code is going to be similar to React.js), I’d recommend using React.
You can use Capacitor.js for instantly shipping a mobile app with your codebase that “just works”. Use Capgo for affordable codepush and you’re set!
HTMX all the way if you’re not building an app cause not everything is an “app”.
At the same time, if you’re building an app with a framework unlike Phoenix, I don’t see why one would not go ahead and use a decent JS framework. Using frontend framework seems to be facing a lot of aversion and I don’t understand if it’s because of the inability to learn these frameworks or what.
Point is, your users just need a snappy app that works. That’s it! And using a robust frontend framework makes it easier.