How to create a mobile app while coding on laptop?

Are you building websites to work on All devices?   In that case, use Bootstrap responsive framework.  It fits all major device sizes (mobile, tablet, laptop, desktop).

https://www.w3schools.com/bootstrap4/

Or is this going to be a dedicated mobile app built specifically for an iPhone, iPad or Android?  And if so, which one?  Be specific as that will determine what kind of code and screen size.

I imply that you do not want to set up a native application, but a PWA.

And even in this case, DW is not the ideal tool for that. Indeed, DW does not take into account almost all the APIs, nor the Javascript that goes with it...

Well, in order to answer your question about the visual aspect of the rendering, although beginning to date maybe these two articles will give you some ideas and should help you :

• https://gbksoft.com/blog/dimensions-resolution-for-ios-and-android-app-design/
• https://buildfire.com/screen-size-resolution-importance/

If however, I had misinterpreted your questioning, please do not hesitate to ask for clarifications or corrections of my remarks.