Well it would be swapping as always when RAM is not enough, and with an SSD you’d probably hardly notice, but it does seem high. ROCK does not swap and 8 GB are supposed to be enough for very large libraries. Now, ROCK runs nothing but Roon server and you’d have to add the overhead for macOS and so on, but nevertheless.
E.g., I found an older thread were people are reporting around 4-7 GB or so on Mac:
Let’s see what official support has to say when this thread reaches the head of their queue.