That looks like 'Smoothing groups' to me instead of normals.
1. Put an 'Edit Poly' on the mesh and go to 'Polygon' subobject.
2. Then select all of the polys with 'Ctrl+A.' Next, go to the 'Polygon: Smoothing Groups' panel and click 'Clear All.'
3. Lastly, "uncheck" the 'Smoothing groups' box in the OBJ export Options dialog.
See if that helps. Sometimes it doesn't and I have to remove the 'Smoothing' in the program the mesh went to, in your case, you may have to remove the Smoothing Groups or assignments from within Marmoset.
Rob Holmes

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3ds Max (2023-2025), V-Ray 6.2, Ryzen 9 3950-X Processor, DDR 4 128MB, Gigabyte Aorus X570 Master motherboard, Sabrent Rocket NVMe 4.0 M.2 drives, NVidia RTX 4090, Space Pilot Pro, Windows 11 Pro x64, Tri-Monitor, Cintiq 13HD, Windows 11 x64
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