Yes, the Fujifilm X100VI 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.)
“Fujifilm X100VI specifications: storage media is SD/SDHC/SDXC with UHS-I interface — UHS-I cards natively compatible with this camera's recording modes.”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)