If you found an online course titled "Well-Rounded Software Engineering," what would you expect it to cover? (I'm starting to build a course with that as its working title.)
This article actually covers a lot of what I was going to suggest. Note how it's almost completely language-agnostic, and that's a good thing. "Well Rounded" means you're looking for a very general outlook, a jack of all trades's view, of SWE. So you can't lock your subject matter into any one language, paradigm, platform, library, etc. That leaves you with the soft/technical skills of engineering as a whole, not just SWE.
So the more technical skills would be Analysis, Critical Thinking, Problem Solving and Troubleshooting, Communication and Presentation, the scientific method, etc.
The softer skills are more social or environmental: Working in a team, Giving and handling criticism, etc.
What do you like to read for work or in your spare time? (That's related to your job or code more generally). Trying to get a list of content that's actually good and read by real people vs propped up by algorithms.
Send links if possible or give names of sites / blogs / creators.
@mariyadelano now and then I wonder how something works, and then I’ll read the RFC for it. After a while it becomes a bit like reading history. Example: RFC 822 is from 1982, but recognisably describes HTTP/1 headers (and it turns out they’re pretty complicated to parse). PNG (RFC 2083) is another fun one to get to grips with.