Shaders actually working is pretty recent so guides are going to be showing you how to use filters, which are slow and yield worse results.
But dear god we finally have shader support and it is glorious. Shut off integer scaling and bilinear interpolation, apply the sharp simple bilinear filter and let the screen be filled top to bottom with pixels sharp enough to cut, without any of that annoying shimmer.
If you want a tiny perfect scale though, all you need to do is in scaling options, integer scaling on, and change aspect ratio to 1:1 PAR. Be sure bilinear filtering and any shaders are off, and you got it.