How do I make a link to a flag edit page?
I'm not sure about any view field for an edit link, but you can link to the flag's edit screen, like most entities, in a number of ways.
Looking at the module's flag.routing.yml file, we see the edit route defined like:
entity.flag.edit_form:
  path: '/admin/structure/flags/manage/{flag}'
  defaults:
    _entity_form: flag.edit
    _title: 'Edit Flag'
  requirements:
    _entity_access: 'flag.update'

The flag argument here is for the flag's id.
You can build out the link to the flag manually, e.g.
&lt;a href='/admin/structure/flags/manage/MY_FLAG_ID'&gt;Edit MY FLAG&lt;/a&gt;

Or if you're working with twig, e.g. rewriting a view's field, make sure you're also including the flag's id in the view then rewrite doing something like:
&lt;a href='/admin/structure/flags/manage/{{ flag_id }}'&gt;{{ &quot;Edit&quot;|t }}&lt;/a&gt;

Or you can use PHP to build the url directly from the route. It's recommended to use one of the following methods if you're working in PHP.
To get just the url text or object in PHP, use Url::fromRoute():
use \Drupal\Core\Url;

$my_flag_url_object = Url::fromRoute('entity.flag.edit_form', ['flag' =&gt; MY_FLAG_ID]);
// $my_flag_url_string returns something like &quot;/admin/structure/flags/manage/123&quot;
$my_flag_url_string = $my_flag_url_object-&gt;toString();

To build the whole link in PHP, use Link::createFromRoute():
use \Drupal\core\Link;

$my_flag_edit_link = Link::createFromRoute('MY FLAG EDIT TEXT', 'entity.flag.edit_form', ['flag' =&gt; MY_FLAG_ID]);