Like a car wheel, the wheel tire in original file is not orthogonal, so I decide to move it up in the air and add a DOP network to let it free fall on the ground, so the end frame is always flat.

But when I create a subnet to export fbx, the model remains in the start position, could someone gime a solution on this? thx!

use Timeshift SOP to hold the frame you are happy with
then afterwards to avoid recomputing whenever you open the file you can cache that either to memory
using Stash SOP to store the geo at the frame you want, especially if it's just about lightweight rbd points for example
or to dist using File Cache SOP or others
or just do your fbx export directly after the frame hold

tamte
use Timeshift SOP to hold the frame you are happy with
then afterwards to avoid recomputing whenever you open the file you can cache that either to memory
using Stash SOP to store the geo at the frame you want, especially if it's just about lightweight rbd points for example
or to dist using File Cache SOP or others
or just do your fbx export directly after the frame hold

thx! problem solved !