This isn't new behavior or tied to assignment enhancements. When the assignment submission type is 'file upload', attached Google Drive files are always converted to a microsoft file. If students submit a shareable url the teacher would be able to see the Google doc. Alternatively, there is the Google Assignments LTI 1.3 where the teacher can see the version history.
From the guide, How do I create an online assignment: "When Google file types are submitted as an assignment submission, those files will convert to their Microsoft counterpart file types and appear in the submission as respective Word, Excel, or PowerPoint files. Canvas uses the conversion file type for submissions (and to render supported file types as DocViewer files in SpeedGrader), so if you want to restrict file types to only include Google file types, you must also include the file types for each respective Microsoft file type as well. For instance, if you want to only allow Google Slide submissions, you must include .pptx as a restrictive file type, otherwise Canvas will not show the .gslide files in the Google Doc tab."
