The "file_validate_extensions" plugin does not exist.

Steps to reproduce

I am using drupal 11.1.1 and install theme with version 1.1.0 and go to the theme setting page and add the slider image but getting issue in networks.

Issue :

Drupal\Component\Plugin\Exception\PluginNotFoundException: The "file_validate_extensions" plugin does not exist.

Proposed resolution

file_validate_extensions() is now removed in D11.

So you can use below code . It is working fine for me.

'#upload_validators' => array(
'FileExtension' => array('png gif jpg jpeg apng svg')
),