6 hours……DONE. Here’s the result, found:
1. If I create a plane in Blender, its texture shows on both sides, so I guess no need to for double sided shader, for now.
2. I made a 4 plane leaf combined with opacity map. It works in Cycles, Eevee (Alpha Blend) and Sketchfab.
Sorry, I’m too tired to type now, This stupid video explains everything.