4k plex

[ed]

If you are streaming locally, transcoding is probably not required. Original file can be played. But if you stream remotely, you may need Celeron CPU for 4K transcoding via built in video app. Transcoding 4k via Plex will be only possible with NAS such as TSH-674 or TS-673A with PCIe GPU card.
Other brands like Synology do not make Plex-friendly NAS.