No, the Panasonic Lumix S5 IIX is not compatible with the Samsung PRO Plus 256GB SD.
Samsung PRO Plus is rated Video Speed Class V30 (not V60/V90) per Samsung's own spec page. Panasonic S5 IIX's own spec sheet requires an SD card with Video Speed Class 60 or higher even for its lowest 4K tier (400 Mbps / 4K30), and Video Speed Class 90 for 4K60 (600 Mbps). V30 does not meet either floor -- still incompatible, now backed by a real citation instead of none.
What works instead
See all compatible camera for the Panasonic Lumix S5 IIX →“Motion pictures with 400Mbps or less: External USB-SSD, SD memory card with Video Speed Class 60 or higher”
Last verified:
Confidence: inferred