Drupal - How do I override the title with the username?

1. Make Fields your format

   

   Alternatively: if you are using the rendered entity row plugin check the Force using fields in the Format | Settings.

2. In RELATIONSHIP, Add Content author

   • Checkmark ☑ Require relationship

3. In FIELDS, add Name

   • Checkmark ☑ Exclude from display
   • Uncheck ☐ Link to the user

4. For TITLE put {{ name }}'s blog

   

   OR you could put it in your CONTEXTUAL FILTER; even though {{ name }} is not listed as a replacement pattern, it works (as long as you do step 1, 2, and 3).

   

Result

BONUS

If you want to capitalize the first letter of the user name use {{ name|capitalize }}'s blog.

You can also add a Rendered Entity as a field.

You can switch the node's uid argument plugin to Drupal\user\Plugin\views\argument\Uid, and get the same behaviour from that field instead. It would take a small amount of code in a custom module.

function MYMODULE_views_data_alter(&$data) {
  $data['node_field_data']['uid']['argument']['id'] = 'user_uid';
}

Alternatively, if passing the author's username in the view URL is not a problem for you, since you have the author relationship set up, you can use the User: User ID field for your filter instead of the one you're currently using. Because of the way its handler treats requests for titles, using {{ arguments.uid }} in the "Override title" field will actually provide you with the username(s) instead of the ID(s).