In the mentioned doc page, in chapter: "Creating and using live CD" I see the text as shown in the attached picture.
It says that the current user has to be added to the group mock.
A few lines further the group is created.
I think the order in which these 2 commands are performed have to be interchanged:
First you create the group,
then you add the user to it,
and finally (but his does not need to be corrected) it is shown that the user indeed is added to the group mock.

[](/fedora-docs/quick-docs/issue/raw/files/3d8e6a0f32b98e66bd3bd816bba85f1fb20454b897f514c7cddda6861a545854-Screenshot_20251125_183843.png)