The main advantage one can get as a freelancer comes down to adding business value. That comes from listening to the customer, then identifying and solving their problems. It doesn’t come from telling customers what they should do or using them to practice with your own preferred languages and tools.
For example a majority of my customers came to me because other consultants refused to (or couldn’t) work with and debug an existing code base and infrastructure. They proposed an expensive and risky full rewrite, which rightly scares customers away. Once I can demonstrate some real value and understand the business I can propose replacing things, and by then I have no competitive bidders to worry about.
For the last ten years I have worked through an agency that connects me with customers. That particular agency represents people who already have a customer base and reputation.