Yes, the Lexar Professional 2000x 256GB SD is compatible with the Panasonic Lumix S5 IIX.
Lexar Professional 2000x 256GB SD is V90 class. Clears: MP4 4K30 LongGOP (72 Mbps, requires V10); MOV 4K/C4K LongGOP (200 Mbps, requires V30); MOV 4K/C4K ALL-Intra (400 Mbps, requires V60); MOV 4K/C4K ALL-Intra (top tier) (600 Mbps, requires V90).
“Panasonic Lumix S5 IIX spec sheet: SD slots compatible with UHS-I/UHS-II Speed Class 3 and UHS-II Video Speed Class 90 standard SDXC memory cards.”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)