I stand corrected! It's 52% that don't even START the first video![0] Other studies report that number at 35%.[1]
One thing that's more consistent are average completion rates hovering around 5%.
[0] https://www.science.org/doi/10.1126/science.aav7958 as cited by [1]
[1] https://openpraxis.org/articles/606/files/66d16716e6c09.pdf
I never got past the second or third lecture in a "Learning How to Learn" class, which I suppose at least meant I had identified the correct problem.
I think the number is probably a bit skewed by the fact a lot of companies offer unlimited access to udemy and such, so people "start" courses without any commitment or cost, and then predictably drop off fast or don't start at all.
Personally I just found none of them really worth doing. They felt almost not genuine in a way, like they cared more about profiting from courses and gaming the system than actually teaching you something. I switched to learning via Youtube videos and found it much more educational than the paid courses.