Processby

The plugin allows you to create and edit the robots.txt file on your site.
<h4>Features</h4>
<ul>
<li>Works with multisite network on Subdomains;</li>
<li>An example of the correct file for WordPress;</li>
<li>Works out of the box;</li>
<li>Totally Free.</li>
</ul>

Robots.txt Editor

Lightweight and perfect for multisite installations.

But in documentation need to say where the option/editor is installed (Settings > Read options).

Perfect!

Gobookmart

GoBookMart Robots Editor is a simple yet powerful WordPress plugin that lets you create, view, and modify your robots.txt file without needing FTP access or coding skills.
Key Features: 
* Create or edit robots.txt from WordPress admin. 
* Auto-generate a default SEO-friendly robots.txt. 
* Save edits directly to your site root. 
* Secure file handling using WordPress filesystem API. 
* Lightweight, fast, and easy to use.
Perfect for SEO experts, developers, and site owners who want full control over how search engines crawl their websites.
Developed by <a href="https://gobookmart.com" rel="nofollow ugc">GoBookMart.com</a>.

GoBookMart Robots Editor

A lightweight plugin to edit or create robots.txt directly from your WordPress dashboard. Developed by GoBookMart.

Robots.txt Editor vs GoBookMart Robots Editor