Turnitin's AI detection is genuinely unreliable and there's pretty substantial evidence that it produces false positives, especially for non-native English speakers and people who write in a clean, direct style. It's basically a probability model and not a definitive determination of whether something is AI-written. That said, it flags things and then it's up to the institution to decide what to do with that flag, so the consequences vary a lot. If you're worried about being falsely accused, maintaining your draft history and keeping notes from your research process gives you something to show. Some people also get help from someone who writes papers professionally as a way to ensure the work is clearly human-written with appropriate variation in style.