I've researched the best online courses for learning about Cryptocurrency. What I've found in summary:

• Khan Academy (Course: Bitcoin: What is it? https://www.khanacademy.org/economics-finance-domain/core-finance/money-and-banking/bitcoin/v/bitcoin-what-is-it) - Academic course including hash functions, signatures, proof of work and security.
• Coursera (Course: Bitcoin and Cryptocurrency Technologies https://www.coursera.org/learn/cryptocurrency) - Technical course including how decentralization works, the components such as blockchain blocks, mining & anonymity. As the assignments are quite technical, I'd say this course is suited to people with a programming background, ideally Java.
• Udemy (Course: Various, see below) - A lot of practical, less technical courses. Subjects include: Getting started (buying, selling, wallets), Investing & Trading, Bitcoin Mining, Bitcoin Certification and a number of other courses focused on niche opportunities. Bear in mind that Udemy is an open platform, which brings with it pluses and minuses: On the negative side, it leaves the door open for poor/dubious content: Always check the reviews! Having said that, there are some good bitcoin courses on Udemy. Also on the plus side, there's a huge variety of subjects and angles that just aren't available elsewhere as convenient, organized courses.

I've documented my recommendations for each type of bitcoin and cryptocurrency course here, in case people are interested:
https://www.smartmoves.life/cryptocurrency-course-recommendations/
Quite a few of the courses are free. I hope you find this helpful!