i see my verts count: 68.8K and tri count: 39.4k on game window stats. when i enable shadow on my light i see my verts count: 165.9K and tri count: 94.9k. is it normal?
It's normal that your polycount would increase, yes. Shadows require an extra render of all shadowcasting objects - including ones that are offscreen but cast shadows onto the screen - so you should look at what your shadowcasters are and how many polys are in them.
I just wonder why when I just enable the shadow (no tick cast shadow on any object). Polygon will double. I though it just count to polygon when it cast shadow from any object?