What is the real rule to have cool UV map for Normal baking?

I have tried to use Substance Painter with Blender.

Imagine to have a cylinder with some bumps and to cut it along one vertical line. You obtain an unwrapped horizontal rectangle in the UV map editor (I haven’t anymore this UV map to show you, but it’s extremely simple to imagine).
In Substance, I have done the Bake and the model looked correct there, so I added bumps, carvings ecc, but when exported and imported to Blender with tangent space (OpenGL) it showed the vertical seam VERY hardly, due to opposite orientation of the normal colors, since the unwrapping goes all around the cylinder but the flat normal maps can’t know it.
So, I solved it slicing the cylinder in 2 parts, by adding a new seam on the opposite side so that I obtained the “front” and “rear” separated UV maps, being able to flip one of them along the X axis to obtain a coherence with the normal red shading. And so, seams are disappeared.

Is this the right workflow? If yes, why do I continuously see tutorials where this stuff is not taken in consideration during the UV map creation?

Or is there a way to “force” the engine to process differently the normal map, in order to avoid seams? In Substance Painter viewer, in fact, seams are not visible in any case. So maybe there is a similar setting in Blender?

i got a bit confused by your explanation, so ill just go through from start to finish.

What you need is:
a High poly object
a Low poly object
a UV map for the low poly object
you do NOT need to UV map the hi poly.

Before exporting, make sure both of the objects has the same ORIGIN POINT
and make sure they are ON TOP OF EACH OTHER

then import the LOW POLY object into Substance painter
click on the BAKE TEXTURES button

then select NORMAL MAP (all the other maps are not needed unless you plan on texturing it in substnace)
then export the NORMAL MAP and import it into blender.

now, you are hopefully using the CYCLES RENDERING ENGINE, and if you do, in the NODE EDITOR, set up the IMAGE TEXTURE NODE and make sure its set to NON COLOUR DATA, and is fed through a NORMAL MAP NODE and then into the diffuse, or glossy node.

now you can turn on Material view, and everything should look plastic fantastic.

Oh well I have tried to create it again to show you an example, but… Now it worked. The fault was of the non-color-data stuff…
For some reaons I was sure to have set it up, that time :confused: And so I have started to think that we have to follow the directions of the colors while creating a UVmap, to avoid seams. It was the only cause…

Sorry and thanks!