Error message : The network connection between your computer and the VPN server could not be established because the remote server is not responding. This could be because one of the network devices (e.g, firewalls, NAT, routers, etc) between your computer and the remote server is not configured to allow VPN connections.

It seems the default state of Windows does not allow you to use IKEv2 due to the incompatibility between your network environment and IKEv2 in Windows.
There are two solutions to this problem.
(1) Use a different VPN method.
(2) Change the Windows settings.
Note! If you make a mistake in the method (2), your Windows will be broken.
We recommend method (1) unless you have knowledge of Windows that allows you to understand the details by looking at the information described below.

The following are the details of each method.

(1) Use a different VPN method
You can also use a method called OpenVPN.

(2) Change Windows settings
You may be able to connect using IKEv2 by changing the Windows registry.
This is a method that may break Windows and make it unusable.
We recommend that you only try this method if you understand the details in the reference information below.
We cannot support you if your Windows is broken.

Microsoft official information
https://support.microsoft.com/en-us/help/926179/how-to-configure-an-l2tp-ipsec-server-behind-a-nat-t-device-in-windows