Just study an MBA.
If your ultimate goal is to be a startup founder, there is no reason to put that as a pre-requisite. If it is to "be in business" or to have a backup plan, then sure.
The point is so you don't waste your time because you've got no idea about strategy and end up building things with no real potential.
It's easy to waste multiple years on side projects that are fundamentally flawed from the start.
Of course an MBA is no guarantee of success, but why do we bother with any education? Hopefully to learn skills and make better decisions.
It's funny how few people here would say a CS degree is a waste of time, but apparently studying business is.
It seems to be some special kind of hubris many programmers have. They're the "clever ones" because they do the building, and sales, marketing, strategy, etc is all so easy or irrelevant it's not worth studying.
Still, ignorance is bliss. You don't know what you don't know.
Strategy, marketing and entrepreneurship are, judging from the posts on here, most lacking. Study those then get started. Study the other modules as you go.
10-15 pounds instead of 10k-15k pounds. If you are the kind of person that needs to be in a (remote) classroom to learn and that is worth 1000 times more, then great. Whatever one needs to do to achieve the goal.
The worlds information is all on the internet. If you don't need the credential, the connections, or the learning structure, everything is free and can be consumed in a perfectly personalized way.
Personally, I would argue that, after a certain point, if you need to pay to get access to that sort of structured environment to learn it's going to be pretty hard to start a company that is, by definition, purely in unstructured space. Also continue to learn because knowledge in those areas is not static, and the things that are just basic foundational info.