Yes, the Fujifilm X100VI works with the Lexar Professional 1667x 64GB SD — with conditions (see below).
Fujifilm X100VI's SD slot is UHS-I only. Fujifilm's own X100VI spec page states UHS-II cards operate in backward-compatible UHS-I mode and meet all recording requirements -- but that's the U3/UHS-I floor, not the V60/V90 UHS-II rating. Lexar Professional 1667x 64GB SD is rated V60, a UHS-II-only guarantee that does not survive that fallback -- no UHS-I-mode or U-class figure is sourced for this card, so real sustained write speed here is unconfirmed. Verify before relying on it for 4K30.
Conditions for compatibility
Falls back to UHS-I mode on Fujifilm X100VI's SD slot -- Lexar Professional 1667x 64GB SD's V60 rating requires UHS-II and does not apply here. Verify real sustained write speed in UHS-I mode before relying on it for 4K30.
“Fujifilm X100VI specifications: storage media is SD/SDHC/SDXC with UHS-I — UHS-II cards operate in backward-compatible UHS-I mode and meet all recording requirements.”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)