In that case the only conclusion I can come to is that something on the system is blocking it. Because it should be able to access it like a web browser can. Also make sure the JRService.exe and JRWeb.exe and JRWorker.exe apps are allowed through both Windows Defender and the Windows Firewall in addition to the main Media Center executable file. You can also try changing the web engine in MC's Options. If it's set on Internet Explorer (which is long gone) try setting to Chromium or even vice versa and see if that helps.
It'd probably be easier to add MC and its JRService/JRWeb/JRWorker executables to Defender's exclusions list and create outbound and inbound rules for them too in Windows Firewall than just straight up disabling both Defender and the Firewall which I would never recommend doing. Taming them by adding the Defender exclusion rules and Firewall inbound/outbound rules and leave them enabled.
Defender taming:
https://yabb.jriver.com/interact/index.php/topic,114101.0.htmlFor the Firewall just create new rules for the Media Center executable and for JRService, JRWeb and JRWorker in both the inbound and outbound rules sections allowing the connection for them, preferably over both TCP and UDP.