Turns out he had literally Windows 10.0, first build lmao. It's all good now, we managed to update it (after a long session of troubleshooting, he was getting a ton of different errors when trying to update normally. MCT and Upgrade this computer did it for him), and Plutonium was successfully installed! Thanks for the help!

N1zle
@N1zle
Posts
-
Can't run Plutonium.exe to install -
BO2 zombies custom game issues0mgsparkle https://plutonium.pw/docs/custom-games/#connecting-via-an-ip-address
"If the friends list doesn't work for you, you can try connecting via an IP Address.
Have the host get their IP (which they can do via the Plutonium Overlay's Network tab, or via WhatIsMyIP)
Then, you will simply be able to connect by opening the console and running the command
connect HostsIPAddressHere
"