how to build mobile apps?

your question is twofold... on the one hand it raises the question about the tool... and on the other hand about languages... so as far as the tool is concerned

as long as you know and are comfortable with languages such as HTML, JavaScript, CSS, JSON, and as long as you master the art of organizing data in an evolving architecture, even in a MariaDB or MongoDB database, you can build and develop anything you want with a tool such as DW.

Indeed, offers a file manager, a code editor, an FTP client, a surface specific to the code and another to the content rendering, plus a multitude of tools that can often be useful as a DOM viewer, an extraction interface, a code fragment organizer, a palette of properties reflecting the object in the selection process, and many others

in short... enough to gather in the same interface everything you might need... but again, it comes down to knowing what you do, with what you do it, and how you do it...

but

DW is no longer at all the registered drag tool that allowed without too much knowledge to build dynamic sites.... Today applications, games and all other type of applications, connected or not, interconnected or not, are located one step above dynamic websites and DW having separated from its major tools, there are several versions already, and not having evolved as it should in this universe, no longer meet the expectations of designers, nor developers who often find better adapted alternative solutions... and even of simple code editor like Sublime, Visual Studio Code, Vim , and more,

and on the language side

no need c#, nor objective c, nor java... for handling web app and pwa... just plain vanilla JavaScript is good enought...

Whether on the server side or the client side, including the management and organization of data in a structured, efficient and fast set, JavaScript has become established today and meets the expectations, combines the most demanding and complex, of application developers.

the polymorphic approach to language, both in object-oriented form (classes or proptotypes... although it is only prototypal), and FP... JavaScript meets all our approaches (even combined)

HTML5, complemented by numerous APIs continuously in response to expectations, allows in a native way, to solve many polymorphic operating system problems.