Yes, the SanDisk Extreme PRO SD UHS-II V90 128GB is compatible with the Sony FX3.
Sony FX3's SD slot accepts SanDisk Extreme PRO SD UHS-II V90 128GB directly. V90 class clears the SD slot's V90 floor required for the camera's top-tier XAVC S-I 4K/HD intraframe modes (600Mbps/222Mbps) — compatible for every recording mode on this slot.
“XAVC S-I 4K 600Mbps CFexpress Type A memory card (VPG200 or higher) SDXC V90 or higher”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)