No, the Canon EOS R7 is not compatible with the Lexar Professional CFexpress Type A Gold 256GB.
Canon's own R7 reference manual: recording media is SD/SDHC/SDXC only, both card slots UHS-II -- no CFexpress slot of any type. CFexpress Type A physically cannot be inserted -- still incompatible, now backed by a real citation instead of none.
What works instead
See all compatible camera for the Canon EOS R7 →“Recording media Recording media SD, SDHC, SDXC memory cards SD speed class Supported UHS speed class Supported UHS-I Supported UHS-II Supported Card slot: Equipped with dual card slots Card slot 1: UHS-II supported Card slot 2: UHS-II supported”
Last verified:
Confidence: inferred