That's just video mode support. That has nothing to do with integer scaling really. I think someone should make a better video on this. But here's one sort of going over it..
https://www.youtube.com/watch?v=HPJFnwKufb0
You don't understand the problem I'm describing to you.
Your screen has 1536 "square" dots vertically.
You are trying to scale up square dots into that display unevenly, so when you do that, some of them are not square. Even with nearest neighbor (which helps), you will still have imperfect squares, merely an illusion to make them look square (unless the division of the source video being scaled into your native resolution of your display equals a whole number).
What you are wanting, perfectly even lines when whole numbers cannot be achieved by division, is mathematically impossible.
Use the integer scaling option if you want good looking scanlines and learn to accept black borders on the top and bottom, or change the filters till you see something you are happy with.
EDIT: For clarity for GBA...
1536 / 160 = 9.6
9 * 160 = 1440
1536 - 1440 = 96.
So you either have 96 pixels worth of uneveness that you are stretching squares out over, or you turn on integer scaling and you subtract 48 pixels from the top and bottom of the screen as a black border.
EDIT2: Another edit since I forgot to mention...
A video mode is not the same thing as a native resolution. If you play on a screen that is 4k native in 1536p, the squares will not be even either.
