This paper reports on a collaborative test of 15 web-based text-matching systems that can be used when plagiarism is suspected. The sobering results show that although some systems can indeed help identify some plagiarized content, they clearly do not find all plagiarism and at times also identify non-plagiarized material as problematic.
https://educationaltechnologyjournal.springeropen.com/articles/10.1186/s41239-020-00192-4