First let’s completely un-install Plex from your system.
Then do a reboot of your NAS
Then install the QTS 1.15.x QPKG you downloaded via App Center - Manual Install
Then point your browser to the following address
http://IP.Of.QNAP:32400
That should start you on the setup of a new server.
If it doesn’t, try SSH’ing into your QNAP (via Putty, etc.) and run this script.
