Submit custom form in Magento 2.3 admin

Your controller should extend Magento\Backend\App\Action and implements Magento\Framework\App\Action\HttpPostActionInterface, also don't forget about ACL.

So should look something like this:

namespace Vendor\Module\Controller\Adminhtml\Folder;

class NewFunction extends \Magento\Backend\App\Action implements \Magento\Framework\App\Action\HttpPostActionInterface
{
    /**
     * Authorization level of a basic admin session
     *
     * @see _isAllowed()
     */
    public const ADMIN_RESOURCE = 'Magento_Cms::save';

    public function execute()
    {
        $params = $this->getRequest()->getParams();
        //OR
        $name = $this->getRequest()->getParam('hello'); 
    }
}

Also don't forget about form_key input, your view should look like:

<form action="<?php echo $block->getNewFunctionUrl()?>" method="post" enctype="multipart/form-data">
    <input type="hidden" name="form_key" value="<?= $block->getFormKey() ?>">
    <input type="text" name="hello"/>
    <input type="submit" value="Submit" />
</form>