Hi @Anonymous User
I believe in the past you could have side loaded Plex in the Developer Mode on the NowTV boxes, but this function was blocked a few years back, so the answer might be no.
Never used Plex so i am not 100% sure of my above answer.
Perhaps if you need Plex consider a full blown Roku player or another device from the list of supported devices from the plex website.
https://www.plex.tv/apps-devices/
