Problem solved.
After switching routers, and in particular with the Orbi, it detected the modem subnet (192.168.1.x) and automatically set itself to a different subnet (10.0.0.x) to avoid conflicts.
On the PC, this in turn resulted in what was previously identified by the firewall as a private network becoming a public network. On the public network, Roon is blocked by the firewall. In my testing I’d only disabled the private network firewall, not realizing it was the public network firewall that was now in play.
Changing the newly defined network to a private network solved the problem. Hope this helps someone else in the future…