I got the answer to my own question from a fellow instructor in my own department. You have to use the people link.
It is not intuitive (at least to me)! I could have sat there all day without it occurring to me to go to the people link for subgroup creation for group assignments. I think it's because I've never done group assignments in canvas where I created subgroups before, so I only ever used the people tab to add individual wait listed students and to conclude non-participating students, and since the time of Covid, to peruse who hadn't been logging into Canvas recently.
After you select group assignments in the discussion assignment creation and select either automatically assign students to groups or check the "I'll create groups later" box, you have to go into the People link on your canvas page. There will be a tab with the name of the grouping category on it, and you click that and the student groups will be listed if you selected automatic group assignments, or there will be a list of all students registered in canvas for this course and the ability to assign sub-group names or numbers.
Once I found this, it was pretty intuitive to figure out how to set the subgroups.
As for assigning a specific article to each student within each four-person group I created, I saw no way to do this. I had to make a "reply" to each individual group of students in the discussion itself and list which student was assigned which link. It took a bit of time, but I copied a template and pasted it, only having to type the names of each student in each group.
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.