Do you think it is interesting to do an online course in order to increase my knowledge?

Yes. There are lots of great online courses in almost any subject area. Keep in mind, if knowledge acquisition is what you are looking for you need to be able to assess what knowledge you have and look for some way of acquiring or adding to that knowledge. Your metacognitive ability to reflect on and assess what you know then to regularly do so when undertaking any kind of course is the most important part of successful learning. You can wander through a myriad of courses and I bet you will learn something of value in all of them, but with the goal to increase your knowledge the next question to evaluate the success of the course is whether you have learned things, gained knowledge specific to your desire knowledge and learning goal.