How to Evaluate iOS App Developers Online Before Hiring?

Hi all!I’m currently searching for the best way to hire iOS app developers online, but I’m struggling to figure out how to properly evaluate candidates. What are the key things I should check when looking at their profiles or portfolios? Are there any specific certifications, skills, or tools they should know? I’d love to hear about your process for hiring developers online. Any red flags I should watch out for? Also, if you have platform recommendations (Upwork, Toptal, etc.), that would be amazing! Thanks in advance for the advice!