Gurm I'm facing the same dilemma actually and am a fellow Plex user.
I've tried the latest Plex desktop client and PMP but both give me a bit of strain, it seems a little 'harsh' compared to older versions.
Maybe try Kodi+Plex add-on? You might be able to use an older version of Kodi with comfortable rendering. Obviously this is really only for HTPC use. I have given up on using Plex on Smart TV's and smartphones because of the obvious (we can't use them!).
It's all or nothing, really. Any online, App-based service like Netflix/Plex et al are going to inevitably want it's userbase to upgrade and update. Also FWIW I can't use any TV sticks or Roku etc, as I'm certain they're running some form of Linux behind it (instant strain like dithering). I even tried a WD HDTV live from 2009 era but even that was uncomfortable.
At least in my situation, Desktop/HTPC or nothing for now 🙁.