I’m my case, students get access to download the HTML files after paying through SendOwl.
An important thing I forgot: you can also just put links to YouTube videos in a text file that is downloaded upon payment. I know people who have made lots of money on courses that are just that. They worried about having something fancier after they had made money.
That said, hosted course solutions are emerging, such as Teachable; however, I personally hate the idea of trusting a VC-backed company to remain in business and to continue having reasonable prices.