Yes, the Lexar Professional 1667x 64GB SD is compatible with the Panasonic Lumix G9 II.
Lexar Professional 1667x 64GB SD is V60 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). Does not meet the floor for: MOV 4K/C4K ALL-Intra (top tier) (600 Mbps, requires V90).
Limitation
Card's speed class is a fixed ceiling -- cannot reach: MOV 4K/C4K ALL-Intra (top tier) (600 Mbps, requires V90). No adapter or setting changes this.
“Motion pictures with 600Mbps or less: External USB-SSD, SD memory card with Video Speed Class 90 -- Panasonic G9 II on-card 4K UHD 59.94p ceiling (600Mbps, the 800Mbps row is External-USB-SSD-only).”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)