Upload multiple resources in Neos Flow

Index.html

<f:form action="upload" enctype="multipart/form-data">
    <f:form.upload name="resources[]" additionalAttributes="{multiple: true}" />
    <f:form.submit value="Upload new resources"/>
</f:form>

SomeController.php

<?php
namespace Your\Package\Controller;

class SomeController extends ActionController {
  
    protected function initializeUploadAction()
    {
        $resourcesPropertyMappingConfiguration = $this->arguments->getArgument('resources')->getPropertyMappingConfiguration();
        $resourcesPropertyMappingConfiguration->allowAllProperties();
    }

    /**
     * @param array <Resource> $resources
     * @return void
     */
    public function uploadAction(array $resources)
    {
      // ...
    }

Note: For more flexibility you should consider creating a custom ViewHelper (that could also allow you to re-display uploaded resources in case of validation error, ...)