Yea as others said it'll be some form of Turnitin software, but it can vary a bit
At my uni you were allowed to edit your submission as much as you wanted before the cutoff time and we were allowed to instantly see our own turnitin reports and get a look, past a certain % it will flag it for human review. Sometimes a highish score (15-20%?) is unavoidable, either through references, quotes, headings or common sentences but it's v quick for lecturer to skim the report and see if there's anything genuine.