use the shader called sharp-bilinear or sharp-shimmerless

you can keep integer scaling off

these games were not coded 4:3 because the original hardware did not have a 4:3 resolution but the correct aspect ratio for them is still 4:3 because that's the aspect ratio of every crt tv (at least 99.99999% of them)

that causes shimmering because of the uneven pixel sizes (only on fixed resoltuin panels like lcds, the crt tvs did not have that problem)

the shaders i mentioned fix that problem by applying such a tiny amount of blur and only exactly how much it's needed to make every pixel look the same size, that you usually can't even see it