Thank you for post!
I understand that you are trying to add Permission under API Permission with the scope you selected user_impersonation and you noticed that status doesn't change to Granted which shows in below screen shot.
As per the document you are referring the admin consent required to use the scope, you can grant the admin consent in same page which is show in below screen shot.
Once you grant admin consent by clicking yes, the status of API permission shows to green which as shows in the bellow.
Hope this helps. Do let us know if you any further queries.
Thanks,
Akhilesh.
If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.