I refuse to take any online course.
I was top at the class at school and college (before I quit). However, I’m the kind of person who can study a subject, pass an exam paper with flying colors, and 3-days later not be able to spell the course title. Alternatively, learning and figuring things out as I go, seems to embed knowledge much better.
Then there is the expense factor. My experience is that only a tiny number of buyers on Fiverr and elsewhere, actually care about qualifications. (Of course in some cases people will.) What top quality buyers seem to look for is proof of past experience.
Learn on the go. That’s what I say. Also, make sure to keep everything you ever write, even if it’s just in a big messy pile. As a basic rule, if you are not horrified by the standard of your own work when you look back a year later, you are not improving as a writer or anything else.
(Of course, there are exceptions to the latter rule.)