No, the Lexar Professional CFexpress Type A Gold 256GB is not compatible with the Panasonic LUMIX GH7.
Panasonic LUMIX GH7's Slot 1 is CFexpress Type B only. Panasonic's own spec sheet states 'Card slot 1: CFexpress Type B card' -- CFexpress Type A uses a physically different, smaller connector and cannot be inserted into this slot.
What works instead
See all compatible memory card for the Lexar Professional CFexpress Type A Gold 256GB →“Card slot 1: CFexpress Type B card Card slot 2: SD memory card / SDHC memory card”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)