Plex Preview App for Roku is simply a ‘Private Channel’. Like any other private channel, it won’t appear in the Roku Guide, but doesn’t have to undergo the Roku Approval Sequence - that could take ‘an eternity’ when you’re waiting for a fix.
If you click the link in every one of these posts, you’ll be whisked away to your Roku Page (after you sign in, of course) and it’ll be right there to add to your device:
Once you have it aboard, it’ll update itself with the up-to-the-minute last version - that can be published in moments, not (what seems like) months.
Track that thread I linked above and when you see a new one, update your Roku and it’ll be there or when your Roku updates daily, you’ll get it.
I don’t even use the Official Channel. I uninstalled it. It’s in the guide if I need it for something. You can however, run both of them side-by-side if you like. They are separate Apps and run independently.