Not enjoying web development. Should I switch to mobile apps?

Switch now. You're doing this for fun, so there's not much reason to force yourself through a whole web stack you aren't excited about.

The JavaScript work wasn't wasted. Functions, logic and asynchronous programming will come up again. Dart, which Flutter uses, may also feel reasonably familiar coming from JavaScript.

Pick based on what you want to build first. Kotlin is a route into Android development. Flutter uses Dart and can target both Android and iPhone, so it's worth trying if you want to explore both.

Make a small app before worrying about having a complete stack. A simple project will give you a better idea of which tools you enjoy using.

You can leave React and Node for later, but don't write off backend concepts entirely. If an app needs to get or store data through an API, understanding that side can be useful. Learn it when a project gives you a reason to.

There's also a middle ground if you like making apps but dislike the particular web material you've been studying. You could try a web app with a framework such as Vue or Quasar and see whether that feels different before committing to a new language.