No, the Lexar Professional CFexpress Type A Gold 256GB is not compatible with the Panasonic Lumix G9 II.
Panasonic Lumix G9 II has two SD-only card slots (no CFexpress support). Its own spec sheet lists 'Card slot Slot 1, Slot 2 SD Memory Card / SDHC Memory Card* / SDXC Memory Card*' — CFexpress Type A uses a physically different connector and cannot be inserted into an SD slot.
What works instead
See all compatible memory card for the Lexar Professional CFexpress Type A Gold 256GB →“Card slot Slot 1, Slot 2 SD Memory Card / SDHC Memory Card* / SDXC Memory Card*”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)