I think learning the basics of subnetting, vlaning, switching, and routing and IOS were the most important parts of it. I don’t think I ever needed to really know how to configure a T1 or various other dead technology. But pretty much every vendor uses a clone of IOS and knowing the proper way to logically configure a network is important. I’ve seen so many abhorrent hacked together networks in my day.
I worked for an ISP who paid for mine back in the day. Took like a 3 day e-learning course and then examine. The real world experience was probably the best way to learn
If you want algorithmic slip then why not just be on corporate owned platforms? The only people that want to feed you slop are those trying to harm you. The fediverse isn’t going to do that, they don’t have a motive for it.