I had Turn It In mark my work as plagiarism some years ago and I had to fight for it. It was clear the teacher wasn’t doing their job and blindly following the tool.
What happened is that I did a Q&A worksheet but in each section of my report I reiterated the question in italics before answering it.
The reiterated questions of course came up as 100% plagiarism because they were just copied from the worksheet.