speedy222

Search every username in your WordPress site from the author. Make the WP Search Username Widget active in your Widgets menu from your WordPress site.
Or place the below shortcode in your WordPress site page content:
[search-username]
Or place the php shortcode in your themes file with a FTP Program. You can find the normal and php shortcode in your shortcodes.txt file.
Option author page with FTP:
Only if you have not a author.php page in your themes then you can upload the author.php page from your plugin directory with a FTP program and save it up your pc directory. And upload it to your themes /wp-content/themes/your-theme-name/ directory with a FTP Program.

WP Search Username

Search every username from the author in your Wordpress site.

nafsadh

Validate Profile Credentials and Names
In a WordPress site users have multiple names in their profile, the user login, display name and nick name. In a multi-user site, there is often a need to keep them unique. You need to allow users have only credible names, such that,
<ul>
<li>All display names are unique</li>
<li>All nicknames are unique</li>
<li>No nickname is a display name or login name of another user</li>
<li>No display name is a nickname or login name of another user</li>
</ul>
Credible Names is a easy plugin to help you with that.

Credible Names

Ensure user's nickname and display name are unique and not a display name or nick name or user name of someone else

WP Search Username vs Credible Names