After recent integration with Google Classroom, Unicheck, a leading plagiarism checker has already announced a new add-on release for Google Docs. For the user this plagiarism checker add-on introduces the same core functionality, combined with several new convenience-level changes involving better document inspection and the shorter time span for checks, advancing the workflow.
https://www.teacherswithapps.com/checking-for-plagiarism-in-google-docs-edit-where-you-write/