I'm facing the same with my GFX100s.
So, from my understanding, Fujifilm would need to provide a firmware update for the GFX100s to allow control via USB-C port. Fuji did provide such an update for the GFX!00 in the past. After all, the X-Series cameras are also compatible with gimbals, such as the Zhiyun Crane 2s, etc.
I sincerely hope Fujifilm will provide a firmware update to enable control via gimbals/USB-C.