No, the Sony FX3 is not compatible with the Sony Tough G 128GB CFexpress Type B.
Sony FX3 has a CFexpress Type A slot. CFexpress Type B is a physically larger format with a different connector — it will not insert into the FX3's slot.
What works instead
See all compatible camera for the Sony FX3 →“This camera supports CFexpress Type A memory cards and SD memory cards”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)