Canvas: Adding a rubric when the assignment uses an External Tool
You can add a rubric to an assignment that uses standard submission types and External tools. However, you must first create the assignment and add the rubric, before returning and selecting the External Tool as the submission type.
Create the assignment and save it with any standard Submission Type.
Save the assignment. You will return to the assignment description page.
Choose Find a rubric (for existing rubrics) or Manage Rubrics (to create a new one).
Save your choice.
Click Edit Assignment.
Scroll to Submission Type and choose External Tool (first dropdown menu).