A free course on Coursera about Bitcoin and Cryptocurrency. All the video links (including timestamps to specific topics) are listed in the Reddit thread linked above.
A free 9-part course provided by Khan Academy which shouldn’t take you more than 2-3 hours to comb through and understand.
A free course provided by Udemy which has 6 hours of on-demand video and 2 hours of on-demand audio. Provides a ‘Certificate of Completion’ if that floats your boat.