You can learn without getting a credential, and you can get a credential without learning. But that doesn’t mean that credentials never match up with an associated learning experience and human capital improvement.
In order for real learning to take place, in general there needs to be three elements: the learning needs to be very specific, there needs to be some form of actionable feedback, and the skill needs to be constantly used after learning it.
Specificity: It is very, very hard – maybe impossible – to teach broad things like “intelligence” or “critical thinking.” Those are descriptive qualities, not skills. Skills are things like calculus and welding. Transfer of learning is a myth; if you want someone to learn something, you have to teach them that specific thing. If you teach someone how to paint a landscape, they won’t even learn how to paint a portrait, let alone how to be a more well-rounded individual, whatever that means.
Actionable Feedback: The better the feedback you get on your work, the faster you’ll learn. If you teach yourself to paint but never study another painter, never get advice, never look at other paintings, etc. you can still improve over time, but you’ll never do so as quickly as someone who does do those things. You’ll probably never reach the same level of skill, either, no matter how long you keep at it. Putting your work into the market is one of the best feedback generators in the world.
Constant Use: You will forget everything you learn if you don’t use it. If you master Spanish in high school (unlikely as that is) but then never speak a word of it in real life, you won’t be fluent in five years. You’ll probably barely be conversational. (Proof of this: Nearly everyone in America has to take a foreign language in high school. Almost no one in America speaks anything besides English an Bad English.)
That being said, if a particular learning environment does have all three of those things – if it teaches a specific skill, gives good actionable feedback, and provides a skill that you will immediately use on a consistent basis – there’s nothing stopping you from attaching a credential to that process.
I don’t have anything against credentials, per se. They’re useful career signals, they can be confidence boosters, and they can motivate you to learn new thing (humans love prizes, after all). But for me, if I’m chasing a credential I want to make sure I’m also actually learning. If that’s true for you as well, then that’s how you should evaluate any program that offers to teach you – if they provide those three things. Otherwise, someone is just selling you a piece of paper.