Hello there, @ErnoMijland ...
I wasn't real sure what you were referring to when I first read through your posting. However, I'm taking an educated guess that you are asking about the "Assign To" options when editing an assignment in your course. It sounds like you would like to assign an assignment to everyone *except* certain students. Is this correct? If so, there is actually a separate area here in the Canvas Community website where you can submit your ideas that you'd like to see incorporated into Canvas. Fortunately, there has already been an idea submitted (way back in 2015) that has gotten lots of comments from Community members all around the globe. The status is currently "Open". Here's the link:
[Assignments] Assign to everyone except selected s... - Instructure Community - 363696
I'd encourage you to follow this idea so that you might have the chance of voting on it in the future.
Please know that the idea process is going through some changes right now, so you'll want to check out this blog posting: Turning Your Feedback into Better Prioritization a... - Instructure Community - 637959
And finally, there's a separate area to submit your ideas. (This area where you posted your question is more for asking questions about Canvas ... not as much for submitting your ideas). Here are Guides for you on how to submit a new idea (though you won't need to submit for your above idea...so as to avoid duplication of ideas):
I hope this will be of some help to you.
