Only fully works with D11?

Problem/Motivation

This module's core version requirement string says it works with Drupal 9, 10, and 11.

In Drupal 11, warnings and preventions both work as expected.
In Drupal 10, I see no warnings, only preventions.
In Drupal 9, the module causes an exception - Drupal\Component\Plugin\Exception\PluginNotFoundException: The "AltTextRules" plugin does not exist.

Steps to reproduce

Create a standard Drupal 9, 10, and 11 site and enable this module on each. Using the default "article" content type, add an image. When prompted for alt text, use the name of the file and save. If this causes a validation error, use "image of (whatever)" as the alt text and save.

In Drupal 11, you are prevented from saving when using the name of the file for alt text, and a warning appears after saving with "image of..." as the alt text.
In Drupal 10, you are prevented from saving when using the name of the file for alt text, but no warning appears after saving with "image of..." as the alt text.
In Drupal 9, this immediately fails as the error is thrown and you cannot enter alt text.

Proposed resolution

Ensure validation behaves as expected in declared versions, or remove those versions from the declaration.