Thanks for your reply, @dylan
My Windows Defender firewall was on. I disabled it for both public and private networks. I also turned off my Avast Premium Security. The system output on the Roon core still skips through all tracks. My network access from my macbook worked though, but, only when playing back to the macbook pro system output. I am also now able to play to my Apple TV. So, a few improvements, but, not being able to play anything on my Roon core still a major issue.