As a high school teacher, the vast majority of assignments, for both my class and those of my colleagues, are submitted through an external tool. That being said, when students do not submit the work, the gradebook does not automatically update the status as MISSING.
I have about 130 students per semester. The amount of time it takes to individually mark each student's assignment as MISSING is absurd and uneccessary. However, it is important for me to do so that the students and their caretakers are aware of their academic progress and what still needs to be completed.
There is an option to set a default grade for students who have not submitted. I can type EX directly for those students who have been excused from the assignment. But there is NOTHING, no "set default status" or even a code to enter to expediate the process.
I have seen many comments regarding this flaw with the gradebook. PLEASE ADD THIS FUNCTION TO THE GRADEBOOK!
First off I am sorry you are experiencing a less than optimal workflow here. If I understand the issue, it is that most of your student work is submitted via and external tool and when they don't turn in their work you have to enter the missing status in the gradebook manually and one off. Again, not to minimize your frustration with this but here in the Q&A area of the community we generally answer questions about how Canvas does or does not work, and/or what work arounds exist or what peoples' workflows look like. We also have the Idea Conversations area which is where people submit ideas for how they would like to see Canvas functionality change. I searched the ideas forum and there are several main ideas to do with the missing status. I wasn't sure if any of them fit exactly with what you are experiencing with assignments submitted via an external tool so I would encourage you to search there as well and either give an existing idea a start rating (aka vote up) or if you don't find something exactly like your experience, create a new one.
An assignment turned in late in Canvas causes the missing assignment status box to be checked. This transfers to the school grade book (Skyward for us) to also have a missing assignment status. Even though a grade is posted in Canvas the missing status remains. It requires a one off removal in Canvas AND in Skyward for the missing status to go away.