Starting soon (April 2). " Drawing Nature, Science and Culture: Natural History Illustration" Its from EdX, so you can audit for free or spend $49 for a verified certificate. I did it last time it was offered and really enjoyed it.
I looked it up, and it looks great! Is it interactive with live instructors, or is it via videos?
It uses videos, which are very well done. There is an actual instructor moderating discussions and answering questions. You do self and peer evaluations of your drawings, and there are a couple of quizzes.
And is it really suitable for beginners?
Yes. They cover very basic stuff. There are quite a few very talented people who take the class, though. Don’t be intimidated.