That cable in the images he posted is just a CSYNC cable without stripper. Retrogamingcables always have the sync stripper on their PCB inside the SCART plug.
Voultar made a video where he recommended a 470 Ohm resistor and 220uF capacitor on the CSYNC line for Genesis cables.
Next step would be to try tweaking the various sync settings in the Sync options menu.
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