This is a really difficult question to answer this without an example. You might want your non GUI content to scale to width, height or both depending on your project.
Using one of the camera scripts helped me a lot, they take a lot of legwork out of this.
Rendercam:
https://www.defold.com/community/projects/84064/
Orthographic camera:
https://www.defold.com/community/projects/76573/
The rendercam page has some nice example screenshots on different ways of handling scale modes for different screen sizes.
Also if your target is mobile, don’t concentrate on specific resolutions - there’s just too many. Your project should fit any resolution from 320x240 (iPhone 1) to 2688x1242 (iPhone Xs Max) and everything inbetween to to be safe.
This is something you have to just try and come back when you’re stuck.