Add a page to the admin where you can upload and download a file

What I would like to do is add a field to an admin page where a file can be downloaded and uploaded. A client would like to upload a csv file that is used by a module developt by an agency that was developing the site before us.

What I have is that I have been able to add a page to the backend, a download and an upload field.

<!-- app/code/Vendor/ModuleName/etc/adminhtml/system.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <section id="modulename" sortOrder="500" showInDefault="1" showInStore="1" showInWebsite="1">
            <tab>catalog</tab>
            <label>Module Name</label>

            <group id="general" translate="label" showInDefault="1" showInWebsite="1" showInStore="1">
                <label>General</label>

                <field id="download" translate="label" type="VendorModuleNameBlockAdminhtmlFormFieldDownload" sortOrder="5" showInDefault="1">
                    <label>Download</label>
                </field>
                <field id="upload_plates_file" translate="label" type="VendorModuleNameBlockAdminhtmlFormFieldUpload" sortOrder="6" showInDefault="1">
                    <label>Upload</label>
                </field>
            </group>
        </section>
    </system>
</config>

And the two files; Upload.php and Download.php.

// app/code/Vendor/ModuleName/Block/Adminhtml/Form/Field/Upload.php
class Upload extends MagentoFrameworkDataFormElementAbstractElement
{
    [...__construtor()...]

    protected function _construct(): void
    {
        parent::_construct();
        $this->setType('file');
    }

    public function getElementHtml(): string
    {
        return parent::getElementHtml();
    }
}

// app/code/Vendor/ModuleName/Block/Adminhtml/Form/Field/Download.php 
class Download extends MagentoFrameworkDataFormElementAbstractElement
{
    [...__constructor()...]

    public function getElementHtml(): string
    {
        $buttonBlock = $this->getForm()->getParent()->getLayout()->createBlock(Button::class);
        $params = ['website' => $buttonBlock->getRequest()->getParam('website')];
        $url = $this->backendUrl->getUrl("*/*/exportPlatesCsv", $params);
        $data = [
            'label' => __('Export CSV'),
            'onclick' => "setLocation('" .
                $url .
                "somewhere/somefile.csv' )",
            'class' => '',
        ];
        return $buttonBlock->setData($data)->toHtml();
    }
}

Now I understand that I need controllers for the actual upload and download action, and I have a app/code/Vendor/ModuleName/Controller/Adminhtml/System/Config/Download.php and a app/code/Elgentos/DownUploadPlatesCSV/Model/Config/Backend/Upload.php. And I have some scafolding inside there, but it does nothing and I wouldn’t know where to begin to fix it.

I know this perhaps isn’t a lot to go by and debugging something on a system you don’t have access to is next to impossible but a nudge in the right direction or an article that covers this use case, which I have not been able to find, would be wonderful! (BTW using magento 2.4.5-p1)