Yes, the Sony FX3 is compatible with the Sony Tough CEA-G480T 480GB CFexpress Type A.
Sony FX3's highest-bitrate movie mode, XAVC S-I 4K (600Mbps), requires a CFexpress Type A memory card rated VPG200 or higher per Sony's own Help Guide. Sony Tough CEA-G480T is VPG400-certified per Sony's own product page -- exceeds the VPG200 floor by a full class. Type A slot confirmed on FX3.
“XAVC S-I 4K 600Mbps CFexpress Type A memory card (VPG200 or higher)”
Confidence: inferred