I just have a fanless computer running Roon,qobuz and separate dac
The Qobuz app (Mac, PC, or mobile) has a built-in facility to download music that be played offline.
To use it, you need to run the Qobuz app as your music player instead of Roon. Music files that you download (Qobuz uses the term "import") are encrypted and can only be played by the Qobuz app.
If you prefer the Roon user interface, perhaps you could switch over to the Qobuz app only while your internet connection is down. You can pre-download (import) enough music on Qobuz to get you through periods when you have no internet.