Why a database marked as “Used by an installed web app” in Plesk cannot be manually removed?

Question

The option Remove Database is grayed out at Plesk > Domains > wordpress.tld > Databases

Why cannot a database marked as Used by an installed web app be marked for deletion?

Answer

Databases marked as Used by an installed web app are created automatically with a web application (such as WordPress, Joomla, Drupal, etc.).

It is not possible to delete these databases separately from a web application.

The only possible way is to remove a whole web application:

1. Log into Plesk.

2. Remove the application in Subscriptions > example.com > Applications.