What is your opinion on online courses, like Skillshare and Udemy? Do you think they are effective in teaching useful skills, or do you think they are not effective?

Well I haven't tried any yet. But I see them as a net positive. There probably isn't always an easy way to verify someone's credentials. But it looks like a way people that are passionate and good at something to make some money showing people what they know, and for people who want to learn a new skill improve their quality of life without breaking the bank.