Thank you for posting and bringing this issue to the attention of the community. I’ve merged your threads since it appears you had duplicate posts regarding this issue.
Officially, Roon ARC does not support VPNs, although some users have specified configurations in VPNs that will allow for port forwarding or other connectivity mechanisms for ARC. Tailscale is the most common solution on this forum, as it functions uniquely from other VPNs, effectively placing ARC in your local network even outside the home.
However, most other consumer VPNs and proxy servers are known to interfere with port forwarding and UPnP, depending on the configuration and rules you’ve set. In most cases, they will block ARC out-of-the-box.
If you try temporarily disabling both for the sake of troubleshooting, is ARC able to autoconfigure port forwarding in Roon → Settings → ARC?
The diagnostic trace you included above shows a 998 status code error; this actually means that your Core is failing to reach Roon’s servers independently of its connection to ARC. The VPN is likely filtering traffic to/from the Core, and you will eventually encounter issues even on Roon Remote in this configuration.
While the #support section doesn’t officially support VPNs, there are many savvy users who will be happy to assist in the #tinkering section if you create a post and specify the VPN you are using in the title.
In the meantime, please report back if ARC port forwarding succeeds with the VPN disabled, and we’ll go from there. Thank you!