We are aware of some issues on macOS Catalina related to file access and security and are working to resolve this problem.
We have seen some suggest a workaround that involves using Terminal commands to get Roon to work. We strongly advise against this as this will prevent your Roon database from working properly once our Catalina issues are resolved.
We appreciate your patience as we continue to work on a fix for this.
Regards,
The Roon Support Team
Workaround,
Start your server in the terminal like this:
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I was advised not to do that by @support because of problems later on…
Here comes the workaround, pls run the following instruction under Terminal. It works for my new OS now.
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This works 
Well done and thanks!!!
Yes! Works perfectly for me too! Thank you Daniel! Brilliant workaround!
Roon tell me that this is not a good workaround since it can cause problems when you want to return to the standard user mode of running Roon. I dont know the details, just that I was told not share this workaround.
But not for Roon Remotes 
So my iMac with Roon Server and external HD containing my music library works. My MacBook Pro works as a Roon Remote after applying the sudo command. Both of these were Catalina upgraded.
But iPhone & iPad as Roon Remotes, no they do not see the library
Tim & Daniel- couldn’t there be another Terminal command run that undoes the workaround when there’s a “final” Catalina upgrade?
It also works for me but unfortunately now I can’t run Roon without entering this sudo command 
It just can’t be opened without it anymore…
See my post above… It is not a recommended workaround as it has other side effects.
Hi all — I’ve moved the above discussion about Catalina workarounds here. Please see my post above, thanks!
type this in Terminal
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it will work, as mine now.
cheers