At the moment there's a lot of development in Linux UI's for mobile devices like Plasma Neon, Ubuntu Touch, Phosh, etc. Is there any way to port the existing app onto such devices. I understood that the app is based on expo, but to my knowledge this doesn't allow it to compile it for the aforementioned platforms. Have you already looked at the Kirigami framework which is based on QtQuick:
https://api.kde.org/frameworks/kirigami/html/index.html
This should also allow cross compilation for Android and iOS.