Yes, the Samsung PRO Plus 256GB SD is compatible with the Sony A7C II.
Samsung PRO Plus 256GB SD is V30 class. Meets the floor for: 4K30 (30 MB/s floor). Does not meet the floor for: 4K60 (60 MB/s floor). (Peak write 90 MB/s is not evidence of sustained performance; the V30 class rating above decides this.)
Limitation
Cannot record XAVC S-I 4K (Intra-frame) -- requires Video Speed Class V90, this card is V30. Works for XAVC HS 4K (Long GOP) and all lower-bitrate modes; card runs at UHS-I speed in the UHS-II slot.
“Sony A7C II Help Guide: XAVC HS 4K at 200Mbps requires SDHC/SDXC U3 or higher; XAVC S-I 4K at 600Mbps requires SDXC V90 — UHS-I V30 card supports standard 4K formats only.”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)