No, the Nikon Z6 III is not compatible with the Samsung PRO Plus 256GB SD.
Samsung PRO Plus is UHS-I, 90 MB/s write per Samsung's own spec page. Nikon's official Z6 III manual requires an SD card sustaining at least 250 MB/s for high frame-size/rate video. 90 MB/s falls well short of that floor -- still incompatible for high-frame-rate modes, now backed by a real citation instead of none. (Standard video recording, which only needs UHS Speed Class 3, is fine -- see the dedicated note on lower-tier modes if/when this body's standard 4K30 floor gets its own pair entry.)
What works instead
See all compatible camera for the Nikon Z6 III →“UHS Speed Class 3 or better SD cards with a maximum data transfer rate of at least 250 MB/s, are recommended for recording and playback of videos with a high frame size or rate.”
Last verified:
Confidence: inferred