Labels, like any activity, only belong "within" a section/topic.
I think how it will be implemented for you depends on your course layout and possibly your theme - such as if all sections are displayed. If you have all sections visible, just add another section at the bottom and change it so that it isn't displayed until a condition is reached. The popup / whatever would be dependent on whether you were able to put in scripts within your label, but you would probably just add HTML to the label I imagine.
You can set access restrictions on a section. Just edit it and fill in the restricted access like you would with any activity. When setting up the restriction, click on the eyeball next to the restriction condition so that the section is hidden until the restriction condition matches.
I think how it will be implemented for you depends on your course layout and possibly your theme - such as if all sections are displayed. If you have all sections visible, just add another section at the bottom and change it so that it isn't displayed until a condition is reached. The popup / whatever would be dependent on whether you were able to put in scripts within your label, but you would probably just add HTML to the label I imagine.
You can set access restrictions on a section. Just edit it and fill in the restricted access like you would with any activity. When setting up the restriction, click on the eyeball next to the restriction condition so that the section is hidden until the restriction condition matches.
Whilst there isn't a 'course completion' restriction built in, if you have the ability to add plugins then you might like to use something like this: https://moodle.org/plugins/availability_coursecompleted (also see https://moodle.org/plugins/?q=course%20type:availability)