Should i mark Sharp edges on my low poly(Shade auto-smooth) or shade smooth for high poly to low poly baking?

Hello ​@Smoky3d,

Interesting question and there are a few things to say.

1. I wouldn’t say triangulation is an absolute MUST DO, but it sometimes helps with your normals indeed. In fact, Painter triangulates your 3D model anyway, even if it’s not clearly visible. However, it will perhaps triangulate the model in a different way than what you would do, resulting with weird shading. If you triangulate it yourself beforehand, you make sure the shading is clean.
    
2. Checking how your normal map looks is not necessarily a good indicator to tell whether there’s an issue or not. I advise you to check the 3D model directly in the “Material” preview.
    
3. If there’s an hard edge or that you’ve marked and edge loop as “sharp” in Blender, you should add a seam in your UVs, to prevent artifacts.

Hope this helps.

Apparently triangulating before exporting from Blender is a MUST DO to avoid the issue a mentioned lastly. My OG question though still remains as if i need to mark any sharps or fully shade smooth and let subd)high poly to low poly bake) do the work.

I'm providing you another example in which case i have a flat surface with a simple bevel of 2 segments with profile shape 1. Without marking sharp edges before exporting the low poly i get this nasty result. Images are with Normal map applied and normal map is at 8192 resolution 16bit. In Substance painter the bake result shows fine.