I am a maintainer for a small open source application that uses the Microsoft Graph API to interact with OneDrive. Recently it stopped working correctly for some file types. After some quick debugging it seems that Microsoft Graph now returns
application/octet-stream as mimetype of an MKV file instead of
video/x-matroska. mp4 containers seem to be unaffected and still return
video/mp4. I had a quick look at the changelog and can't find such change.