database configuration is not supported by Drupal Reset

The database needs to be called "default". For the actual code, see ::validateIsSupported().

Looking at validateIsSupported(), why does it look for $database['default']['prefix']['default']?
Shouldn't it look for $database['default']['default']['prefix'] ?

Looking at

validateIsSupported()

it seems to look for $database['default']['prefix']['default'].
Shouldn't it look for $database['default']['default']['prefix']?

My db infos are defined like this :

$databases['default']['default']['database'] = "db";
$databases['default']['default']['username'] = "db";
$databases['default']['default']['password'] = "db";
$databases['default']['default']['host'] = $host;
$databases['default']['default']['driver'] = $driver;
$databases['default']['default']['port'] = $port;
$databases['default']['default']['prefix'] = '';

Drupal is ok with this, and it seems to be the recommended format.

Yes, it looks like it is not checking correctly. I would welcome a patch to fix it.

It should allow for the prefix setting to be either empty or a string. Look at default.settings.php as it comes from Drupal core and configure your site to use $databases exactly as it appears there, but with your config, and then make it work with that.

I've created a patch that fixes the compatibility check and the dropDatabase command.

Thanks for the patch.

It should be OK for the prefix to not be set.