Shameless plug: I wrote this a while back
There are some ideas I had put in there. Some online sources will be looking up random projects via your favorite search engine. “How to be a Windows administrator” or “how to be a Linux administrator?” are viable searches.
I would also look at “networking fundamentals” or “networking basics”. Dan’s Courses has great networking content and Eli the Computer Guy has still relevant content.
Also Professor something, Messer?
Has a ton of content for free, too.
https://github.com/PowerShell/PowerShell/tree/master/docs/learning-powershell