Seems to be a normal orientation problem already in the lowpoly . Did you checked with Overlays --> Face Orientation (no mix of blue and red).. ohh wait -- you have n-gons in lowpoly.. not so good..
@Andermaiden : In a way you were only partially incorrect (or partially correct depending on the way you look at it :D ) • Lowpoly meshes can indeed be used as placeholders for transferring data. That's a pretty advanced technique though (using a lowpoly as a proxy by baking normals data down to it in Object Space,…