Yea, the Google integration has not been working for me either. It used to be when adding Google Drive to "registered services" it would be at the tab for submission when students added it (but I might be mistaken, it has been a while).
My workaround if I want a Google-type submission (Docs, Slides, Etc) is to allow for the website URL submission type. The students can get the sharable link (have them mark it so people with the link can comment) from their Google Doc or Slide and post that in the URL section--- while it does not do the conversion to PPT or Docx that the integration does, it will load the webpage (click the link and it should load) you can still see all of this in the speed grader.
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