I remember having difficulties with the iOS app, but before I came here to tell you that I wanted to double check. What I found delighted me. The iOS app works entirely fine except for a small issue where while playing media, you can't expand the player controls and read them with VO. You need to pause the media and then expand the controls. Otherwise the app stops working with VO and it's an issue until you close the app out from app switcher and start again.

However, it works awesomely on Mac. I recommend using Chrome with it instead of Safari though.

Happy to say that the iOS app is mostly accessible. There are a few focus issues with voiceover, mainly pertaining to entering in pin numbers where voiceover can focus around them, but every element seems to be labeled. File names read out properly, and the media player has no unlabeled elements.
I haven’t used it in a little bit, but hope this is helpful. Last time I checked the app was about three months ago.

I’m low vision and not fully blind, but I would be happy to answer any questions you may have or try out anything you may need! I extensively use Plex daily.