I use Blender 2.8 on Mac OS.
Create a cube, in editing mode I do UV scan, UV editor shows it, click open image, choose. It shows it in the UV editor, but does not display the texture on the object in any mode (how to fix it?)
Textures Added by nodes are displayed in the materials, but this spoils the aspect ratio and stretches, I think to solve the problem using UV (or can be fixed in materials?).

Answer 1, Authority 100%

Click here (ViewPort Shading – Color – Texture):