Agreed, this is definitely not a solution. I have been using my surface with a dock as my desktop PC for two years now. Canvas has worked with that configuration up until this week. It is clear that they have recently introduced a bug that mis-identifies my computer as a tablet.
Aslo, it's not acceptable that they do this with windows tablets at all! They do not offer a native windows client, so that basically means that where I was able to use my surface pen for inking, now I cannot grade assignments in tablet mode. So their bug has also removed a major feature that I made extensive use of.
Instructure, please be more careful. As a professional software engineer and professor of computer science, I can say with all authority and confidence that you have made a terrible and preventable error. There is no excuse for production releases which break broad categories of computers.