Yep, it doesn’t really make sense preloading the queue with potentially thousands of tracks … On the queue page, checkout the Roon Radio panel … it displays “Shuffle” and “Shuffling”.
If you go to your tracks page and focus on all played, then reverse that so it shows all not played, then shuffle that. Save it as a bookmark and it will always be every song in your library that hasn’t been played. At some time in the future, Roon will let us edit play counts so you can reset your library when you’ve played every song. Of course you can add focus elements to further restrict your bookmark. I generally don’t include xmas music.