To me personally, this is the best comment I've read in my time on HN since 2011 or so. I am also building a learning platform as potential lifestyle business, having been a user of such platforms and worked in large corporate I fully understand that the groups you identify are absolutely true. One important point is that you can make successful business helping people prepare for the certificates without being the issuing party - not VC level, but still. This way you can cover some of the checkbox checkers and self-motivated learners at the same time.
Self motivated learners who will be willing to pay you can also be groupped in a few groups - the ones seeking future employment in tech sector, looking to understand the technology better and showcase it on their resume with some projects that your platform will allow them to complete and ones doing this purely for fun or to keep up, I believe the latter group is very small.
Platform alone, even with tons of learning materials will not be enough to get this off the ground, you will either need to leverage your existing audience, bringing us back to the fact that everything is an attention economy now, or, you'll need to be very advertisement heavy on YouTube, which you can bruteforce with VC investment, see skillshare for example. NordVPN took off the same bruteforce way, although in a different product category.
My platform will combine technical learning with in-material challenges, sort of a sprinkled leetcode if you will. The idea to implement a LLM side-tutor also crossed my mind.