Forget about this video.
Correct way which will surve full pipeline (in case if needed) without getting artifacts in shading of Blender > Baking&Texturing (marmoset toolbag/substance painter/anything else) > Unreal Engine:
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Make sure you enable Auto Smooth and set it to 180deg, when set your hard edges where needed
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Export with Smoothing: Edges. Also check Tangent Spaces
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dont forget to triangulate your model before exporting
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In UE set Normal Import Method: Import Normals
In case you baking you baking in Toolbag, make sure you using MikkT space. Not sure about Painter/xNormal/something else cause im only use Toolbag. But if MikkT space option are exist - use it.