Yes, the Sony FX3 is compatible with the Sony SF-M Tough Series 128GB SD UHS-II.
Sony FX3's SD slot accepts Sony SF-M Tough Series 128GB SD UHS-II directly. V60 class meets the V60 floor for standard XAVC HS/S 4K (280Mbps) but never reaches the V90 floor the camera's top-tier XAVC S-I intraframe modes (600Mbps/222Mbps) require — no setting or firmware update changes a card's rated speed class.
Limitation
Cannot record XAVC S-I 4K (600Mbps) or XAVC S-I HD (222Mbps) intraframe modes on the SD slot — those require SDXC V90 or higher. Works for XAVC HS 4K / XAVC S 4K (280Mbps) and XAVC S HD (100Mbps) on this slot.
“XAVC HS 4K 280Mbps CFexpress Type A memory card (VPG200 or higher) SDXC V60 or higher”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)