Hi Alan,
Roon doesn’t have a folder browser view in it’s User Interface and there is no shortcut to send a track to Roon to play from an operating system folder browser.
There is a Feature Request thread here for a folder/file browser within Roon and another here regarding a folder view as a Filter.
I don’t recall seeing a Feature Request for a shortcut to send a track to Roon from an OS browser. It sounds like a good candidate to start one and see what the devs and other users think. I suspect that the compilation folder would have to be within a Roon watched folder for that to work.