Yes, the Lexar Professional 2000x 128GB SD UHS-II is compatible with the Sony Alpha A9 III.
Lexar Professional 2000x 128GB SD UHS-II is V90 class. Clears: XAVC S HD (100 Mbps, requires U3); XAVC HS 4K (280 Mbps, requires V60); XAVC S 4K (280 Mbps, requires V60); XAVC S-I 4K (600 Mbps, requires V90); XAVC S-I HD (222 Mbps, requires V90).
“This camera supports CFexpress Type A memory cards and SD memory cards (UHS-I, UHS-II compatible).”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)