This is what I used when I first learning: https://serversforhackers.com/

For a really good practical project: build a website, then host it on your mini-PC and find a way to expose it to the internet. This will teach you a lot about DNS, proxying, building websites, managing the server (via some config management or container), monitoring, etc.

Thanks for sharing this. It is incredibly useful!

Then remember that we live in 2024 and that you need to learn how to do DevOps, not sysadmin