How to practice system design without a study partner?

I'm trying to level up my system design skills, but I don't have a study partner for mock interviews, and the paid platforms can get expensive quickly. I'm looking for effective solo practice strategies. What are some good ways to practice system design by yourself? I've tried writing out designs on paper and talking through them, but it's hard to get objective feedback. Has anyone had success with recording themselves, or using specific tools that simulate an interview environment? Are there good feedback loops for solo practitioners? I want to make sure I'm not just reinforcing bad habits.