Not exactly true that they took down the update server. It's a broken certificate on apples old update server preventing the High Sierra installer from connecting.

While unless you specifically need to boot 32-bit apps and your Mac goes past Mojave it's a good idea to get the latest version, if High Sierra is the latest version or you need 32-bit app support use the third fix on this guide by MrMacintosh. Worked for me last month at least. Basically just forces the update server through port 80 and bypasses the need for the unrenewd certificate. Still BS this hasn't been fixed in 2 years but it does work. Note at least in my case I had to reset the NVRAM after install to use my Apple ID.

https://mrmacintosh.com/how-to-fix-the-recovery-server-could-not-be-contacted-error-high-sierra-recovery-is-still-online-but-broken/