I'm getting a message when installing launcher or whatever.. "Couldn't find an installed template that matches the input, searching online for one that does...
[uMod] 02:52 PM [Error] No templates found matching: 'umod-unity-windows-launcher'.
[uMod] 02:52 PM [Error] To list installed templates, run 'dotnet new --list'."

And I can't figure out what to do..

All that step does is create a bat or sh file for you, you can use any.

Also please keep in mind that uMod is not released and is only intended for testing at the moment, Oxide is for live servers.