Your Unity asset 3D model flickers during manual retopology mainly due to overlapping geometry (z-fighting) or incorrect vertex normals.
Overlapping faces/edges make the renderer struggle to prioritize surfaces, causing flicker. Flipped or inconsistent normals disrupt light shading, also leading to flicker.
Fix it by using your retopology tool (e.g., Blender, Maya) to remove overlaps, then recalculate normals (look for “Recalculate Normals” or “Flip Normals”) to ensure they face outward consistently.