cazadescuentos VS SlinkyDemos

Still, you don't need to because you can write a simple Scala.js PWA that gets deployed to the Play Store as a Trusted Web Activity, it is a super nice experience (here is one example).

I'm biased to monorepos, check the template I posted above because it does exactly that, I even have a monorepo that includes a browser extension sharing code with backend/webapp

cazadescuentos-chrome: a price-tracker browser extension.

Slinky does support react-native but I haven't tried it, the app I was referring to is this pwa with this small android wrapper (playstore link), the android wrapper was mostly auto-generated and it just have a small update to support sharing data to it from the browser, I understand the same can be done for iOS but I haven't tried just because I don't have a Mac.

Given that you want interoperability with js, I'd start by playing with https://scalablytyped.org/, then, play with the scalajs-react demos (https://github.com/ScalablyTyped/ScalaJsReactDemos) and the slinky demos (https://github.com/ScalablyTyped/SlinkyDemos). There are some libraries that scalablytyped doesn't support pretty well but you can leverage https://github.com/nafg/scalajs-facades for those.

See for instance this demo source, deployed through expo, which uses a bunch of third party libraries like antd component library, react router, web view, custom fonts, playing audio, etc.