If you are in a hurry to learn something new, your best bet is probably just to pay someone who’s knowledgeable in the subject and in pedagogy to train you.
But if you aren’t in a hurry (and for most of the things we’d ultimately like to learn, we really don’t need to be in that much of a hurry), it is possible and even enjoyable to teach yourself about what you want to learn. You may not perfect your knowledge in this way, but you can do a lot of the work without much help.
Here’s the key, from what I’ve found: you need to have access to a lot of different resources. You need an abundance of resources to compare. In the internet age, we generally don’t lack for options, and that is excellent for the autodidact.
Most of the available resources will be either of poor quality or else tailored to someone at a different level. That’s okay. We need patience to work our way through the mountain of unsuitable resources to find the perfect few. In the process of sifting through the wrong resources, a picture of the subject you want to learn is already beginning to form in your mind.
And then at last you find one or two of the perfect resources! A website, or a YouTube channel, or a book. What next? Use them, of course, until you get frustrated or overly bored. Then go back on the search. Eventually you’ll probably circle back to some of the earlier resources, might work through some of them multiple times.
It takes gigantic patience and persistence to learn a subject in this way. On the other hand, if you can do it, then you can learn at your own pace, you can learn as widely and as deeply as you choose, prioritizing the aspects you want to prioritize. You can get the education of your dreams without spending a dollar.
All you need is a little fragment of your day, invested again and again, for as long as it takes.