Hi @MisterTay ,
Try assigning it to that one student FIRST, then use the +Add feature and select "Everyone" for that option. When I did this, the text changed to "Everyone else" in the upper box. Since the assignment had already been assigned with different settings to the individual student, he was removed from the next set.
To prevent the student from completing the assignment, set the Available date to some time far in the future (or the last day of the term if you have to stay within a grading period) for that student.
If your institution allows you to create sections, you also could make a section with just the one student and another section with everyone else. Then assign based on section. This method may cause issues with syncing to an SIS, so be aware of any limitations with your Canvas/SIS integration.