Which to upload your course will save you a lot of headaches since the platform is already created, you forget about updates, server crashes, technical problems and attention to this phone number list aspect with your students, so the integration of payments and failures with them, etc. These platforms, for their part, optimize marketing and are interested in having them buy the courses on their platforms. In addition, many students from other courses will know you more easily.
Using these platforms you don't start from scratch because they already have many visits . For all this, I usually recommend creating your online course and selling it on one of these platforms such as Udemy, Tutellus or similar. You lose a little control of your courses and prices but you can start making sales more quickly even though you have many competitors on the same platform and you must differentiate yourself well. You can also opt for platforms such as Hotmart, Cursify.