I use Udemy, Coursera, and others free learning source from the internet and I do think Udemy is a good one, though I never subscribe to them. If you're looking to learn about crypto, you should try to read free books like Mastering Bitcoin, you can download it from a lot of sources.
Alternatively, you can learn a lot from here (about crypto):
https://github.com/cmahon/awesome-cryptocurrency. Most resources are books btw.