Hello there fellow Canvas educator!
Here are some helpful tips/tutorials for setting up Kami assignments. I have done a lot of current research on using this in my High School Math Distance Learning courses lately. I hope this helps for desktop/laptop/chromebook use. I am still looking into the mobile device options. I am not sure students can successfully use the external tool on their Student Canvas app?
Kami (webinar) VERY HELPFUL...downloading, canvas assignment, student use, submission
How to submit a Kami EMBEDDED assignment (NEW Aug 2020)
https://www.youtube.com/watch?v=nRwGrrdEBYA
RUBRIC must be added to assignment BEFORE making it an external tool (I also add a screenshot of the rubric in the instructions so that students can see the Rubric while completing the PDF): Adding a rubric to an External Tool assignment >>> create the assignment as a regular online submission type, save it, add the rubric, and then change the submission type to External Tool.