I think most of the videos you’re going to have to pay for online on websites like Udemy can be gotten for free on other platforms like YouTube, although you might have to be doing some deep research to find exactly what you’re looking for.

The good thing about the platforms where you have to pay for them is that the particular subject you want to learn will have everything about it arranged in one package and you will learn everything that you’re supposed to learn, unlike YouTube where you will have to be searching for them and might not even be aware of some important things you have to learn and ignore them. You can find courses about blockchain on all these platforms.