My process so far has been I keep a daily journal where I write down the most interesting things I learnt or did everyday. If my daily notes are getting unwieldy then I use a Markdown file which I sync on Github. And when I really want to make sure that I've understood something I'll either write a blogpost or stream myself going through a library.
I would definitely appreciate the ability to search my old notes better since they got too long to efficiently parse a long time ago but this process lets me structure the really important concepts I learn without adding too much overhead when I'm just learning random stuff. I also expect my notes to outlast many knowledge base projects and part of the appeal of markdown to me is that it's probably gonna be around for a while.
I'm curious if any writers here have found personal knowledge bases to be worth the initial overhead.