On Overview the Connect address is shown as address:port. Both parts matter, and the port is not the Mumble default. In the Mumble app, Server, Connect, Add New, enter the address in Address and the number in Port. A wrong port gives Connection refused or timed out. See How to connect to your Mumble server.
3. Server password
If you set a join password, Mumble asks for it. A wrong password shows an Invalid server password message. See How to set a join password.
A VPN or school or work network can block the port. Try a mobile hotspot to test.
Mumble uses TCP for control and UDP for voice on the same port. If voice is missing but you connect, a router or firewall is blocking UDP. Mumble then falls back to sending voice over TCP, which is fine but can add delay.
Antivirus or a Windows firewall prompt may need allowing for the Mumble app.