Yes, the Nikon Z fc is compatible with the Samsung PRO Plus 256GB SD.
Samsung PRO Plus 256GB SD is V30 class. Meets the floor for: 4K30 (30 MB/s floor). (Peak write 90 MB/s is not evidence of sustained performance; the V30 class rating above decides this.)
“Nikon Z fc specifications: storage media is SD and UHS-I compliant SDHC and SDXC memory cards — UHS-I card is natively compatible.”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)