Set available paragraph type(s) on a paragraph field

Our reference handler has two settings, to also control order as well as the inverted stuff. I recommend to change the settings through the UI and then diff the changes with config import/export.

That does not really answer my question, as I wanted to set the available paragraphs in a paragraph field using code only, not the UI.

That said, I figured out how to do it with code alone.

As @berdir mentioned, there are two handler settings (target_bundles and target_bundles_drag_drop). The target_bundles_drag_drop setting needs to be configured. Here's an example implementation, in case someone else needs it.

$field_definition = \Drupal::entityTypeManager()->getStorage('field_config')
    ->load('node.' . $content_type . '.' . $field_name);

// Ensure the field exists and has the target_bundles setting.
if ($field_definition) {
    // Get the handler settings, which contain 'target_bundles'.
    $handler_settings = $field_definition->getSetting('handler_settings');

    // Define the allowed types with their configuration.
    $target_bundles = $handler_settings['target_bundles'];
    $target_bundles[$paragraph_type] = $paragraph_type;

    // Define the target_bundles_drag_drop structure.
    $target_bundles_drag_drop = $handler_settings['target_bundles_drag_drop'];
    $target_bundles_drag_drop[$paragraph_type] = [
        'enabled' => true,
    ];

    // Define the handler settings.
    $handler_settings = [
        'target_bundles' => $target_bundles,
        'negate' => 0,
        'target_bundles_drag_drop' => $target_bundles_drag_drop,
    ];

    // Update the field configuration.
    $field_definition->setSetting('handler_settings', $handler_settings);

    // Save the updated field configuration.
    $field_definition->save();
}

Automatically closed - issue fixed for 2 weeks with no activity.