As your library increases, or as our system requirements grow, you can benefit from more RAM. However, more RAM will prevent crashes (if you are having them) and not increase performance.
On Roon OS, 4GB is more than enough for about 90% of Roon subscriber’s libraries. Another 9.9% could use 8GB. The remainder will need more but are going to have a bad experience anyway due to the experience not being optimized for that much music.