I'm experiencing the same issue with forge-1.16.5-36.1.13-installer. I see in the installer log that there are time outs, however I can ping the redirect URLs. So it appears ICMP is working. But I am not sure if maybe a DNS record is just pointing to the wrong IP? I've attached my log as well for reference.
Thanks
forge-1.16.5-36.1.13-installer.jar.log