PLEX is working great on the WiiM home app on my iPhone 15 plus streaming to my WiiM ultra.
It would be good if you had full usability of Flex, I have Plex Pass so have all the features including 10 radio stations (Artist Mix Builder / Album Mix Builder / Library Radio / Deep Cuts Radio / Time Travel Radio / Random Album Radio / Discovery Radio / Style Radio / Mood Radio / Decade Radio) whereas for Plex in the WiiM app I only have 5 (Library Radio / Deep Cuts Radio / Time Travel Radio / Random Album Radio / Discovery Radio)
Mood Radio is a must have in my opinion.