It was always so, but in the past the server was integrated into the Roon Core. Since the November update the server is simply separated out into its own process. It’s all explained here in the release notes:
200K tracks falls into the „very large library“ category, so non-trivial resource usage is probably to be expected.
If 12 is normal on Mac, I don’t know. Is it growing over time after you reboot? Some people have reported possibly memory leaks. And how much RAM do you have?