Mobile development is really hard according to my experience. You need optimized models,textures, baked lighting, no unnecessary coding, correct and optimize material setup. It can change what type of game you want to make. But they are the steps that i check every time. I learned a lot by trying and getting error and there is also tons of tips and tricks you can find for every different problem (lighting,texturing…) Your game looks different on mobile you said. Maybe you didn’t check it in engine by with mobile preview? Mobile Previewer | Unreal Engine Documentation
And for optimization tips, this helps a lot.