Unable to disable Seven

There is something you could try. Uncomment line 642 in settings.php and rename to seven. clear cache and try again :)

This part ?

/**
 * A custom theme for the offline page:
 *
 * This applies when the site is explicitly set to maintenance mode through the
 * administration page or when the database is inactive due to an error.
 * The template file should also be copied into the theme. It is located inside
 * 'core/modules/system/templates/maintenance-page.html.twig'.
 *
 * Note: This setting does not apply to installation and update pages.
 */
# $settings['maintenance_theme'] = 'bartik';

Forgetting Drush for a moment, can you please describe in detail precisely what happens when you try to disable the theme in the Appearance UI?

I click on the link "Disable", and after that the theme stay in active ones, but the link "Disable" disappear.

That screenshot above does not describe the bug in enough detail. Please post a screenshot of the entire Appearance page, including showing which theme is set as the administration theme.

Here the other part of the page.

Adminimal uses seven as a base theme: https://git.drupalcode.org/project/adminimal_theme/-/blob/8.x-1.6/admini...

You can't disable it.

Also note 🐛 Deprecated core themes cannot be disabled on the "Appearance" tab because they are hidden Needs work .

Thanks for #8. Perhaps it could be useful to add an indication on appearance page and/or Drush about this dependance ?

Have a good day.

Maybe. You have not shared the screenshot I asked for.

this ?

YES! There is no uninstall link because you can’t uninstall it. I agree it would be nice if it said “required by Adminimal theme”.

That could be a good feature request if none exists: “Base themes should display if they are required by another theme”.

But deprecated themes my be a special case which relates to 🐛 Deprecated core themes cannot be disabled on the "Appearance" tab because they are hidden Needs work .

Here we are :)
Will see if info about dependency on deprecated theme will be added so. Cross finger.