User profile form to use admin theme

Hi All,

What would be the best way to force /user/{user}/{profile_type} to use the admin theme?

At the moment I'm adding the following option to profile.routing.yml

options:
  _admin_route: TRUE

It works, but it's a hacky, temporary solution, as I have to hardcode the actual module. Could you guys point me in the right direction?

Would it make sense to have a checkbox option in the back-end /admin/config/people/profile-types/manage/{profile_type} to determine whether a form should use the admin or the default theme?

Thanks