Hi tannu I know something about art course. I will share my knowledge with you. Hope it would be useful.
If at all possible, the number one place you should be selling your online course is also the number one place you should be selling your art: on your own website. This allows you to retain customer information as well as 100% of the profits. There are also dozens of online teaching platforms that will help you quickly create a course and sell it through their website, but be advised that they will take a cut of your profit and you may not be able to retain access to customer information for future marketing.
You can make short YouTube videos and also you can help students for their projects also.In this way they will get to know you and after that you can sell your paintings.I hope this is not absurd answer