module-vendor-notes/Block/Adminhtml/Form/Field/VendorMapping.php

<?php
namespace Shopkeeper\VendorNotes\Block\Adminhtml\Form\Field;

use Magento\Config\Block\System\Config\Form\Field\FieldArray\AbstractFieldArray;
use Magento\Framework\DataObject;

class VendorMapping extends AbstractFieldArray
{
    /**
     * Initialise form fields
     *
     * @return void
     */
    protected function _construct()
    {
        parent::_construct();
        $this->setTemplate('Magento_Config::system/config/form/field/array.phtml');
    }

    /**
     * Prepare rendering the new field by adding all the needed columns
     */
    protected function _prepareToRender()
    {
        $this->addColumn('vendor_name', [
            'label' => __('Vendor Name'),
            'class' => 'required-entry',
            'style' => 'width:200px'
        ]);

        $this->addColumn('note', [
            'label' => __('Note'),
            'class' => 'required-entry',
            'style' => 'width:400px'
        ]);

        $this->_addAfter = false;
        $this->_addButtonLabel = __('Add Vendor Note');
    }

    /**
     * Obtain existing data from form element
     *
     * Each row will be instance of Varien_Object
     *
     * @return array
     */
    public function getArrayRows()
    {
        $result = [];
        /** @var DataObject $row */
        foreach (parent::getArrayRows() as $key => $row) {
            // Ensure row IDs are prefixed with a non-numeric character
            if (is_numeric($key)) {
                $key = 'row_' . $key;
            }
            $result[$key] = $row;
        }
        return $result;
    }

    /**
     * Prepare existing row data object
     *
     * @param DataObject $row
     * @throws \Magento\Framework\Exception\LocalizedException
     */
    protected function _prepareArrayRow(DataObject $row): void
    {
        $options = [];
        $row->setData('option_extra_attrs', $options);
    }
}