Most player software can export the Playlist you have curated into a file, m3u, which can then be imported by a different player software and used or modified. The OP is upset that playlists created in Roon cannot be so exported, even though, Roon can import such files from other sources.
So, playlist from JRiver, exported to file, imported into Roon, modified, is now stuck in Roon and cannot be exported out to go back to JRiver.