To follow up, I did have to use "userid" when I tried to create another URL with a Variable, but in this case, the link actually did show "userid" and not just "id"
I added the example into the docs:
https:// moodlesite.com/grade/report/user/index.php?id=00000&userid=0000 is the path to a user's course user report
https:// moodlesite.com/grade/report/user/index.php is the base URL
?id=00000 is the first added parameter, so type id in the parameter box and in the dropdown select id under course
&userid=0000 is the second added parameter, so type userid in the parameter box and in the dropdown select id under user
I added the example into the docs:
https:// moodlesite.com/grade/report/user/index.php?id=00000&userid=0000 is the path to a user's course user report
https:// moodlesite.com/grade/report/user/index.php is the base URL
?id=00000 is the first added parameter, so type id in the parameter box and in the dropdown select id under course
&userid=0000 is the second added parameter, so type userid in the parameter box and in the dropdown select id under user