I created a texture with opengl (photo on right) and pass it to unity via shared area. If I look at it from a little distance (left photo) though, it looks bad.
I have tried increasing the resolution, changing the MipMapBias, the different filters but nothing
Uhm, sure. What exactly would you expect when you draw lines that are one pixel thick and you view the texture at a resolution that is smaller than the original texture. It’s literally impossible to draw pixels between pixels. Mipmapping does not really help here as there is just too little information in your source texture. So there’s not really a solution here. Is that actually the content you want to generate or is that just placeholder stuff?