I have upgraded both of my NAS units.
With the 765 the Roon Sever has disappeared from Apps Center.
It was there with previous version 5.X
I was able to download the installation package and all works fine now.
So be ready for a surprise.
Apart from that all is fine.
QNAP generally only includes apps in the App Center that have been verified to work with the current version of the OS. You should be able to go onto QNAP’s website, download the Roon package and install it manually.
https://www.qnap.com/en-us/app-center/?os=quts_hero
Roon is there.
Thank you.
This is exactly what I have done