ext_tables.php
<?php
/** @noinspection PhpFullyQualifiedNameUsageInspection */
defined('TYPO3') or die();
/** @var \TYPO3\CMS\Core\Imaging\IconRegistry $iconRegistry */
$iconRegistry = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Core\Imaging\IconRegistry::class);
$iconRegistry->registerIcon(
'extensions-mediaoembed-content-externalmedia',
\TYPO3\CMS\Core\Imaging\IconProvider\SvgIconProvider::class,
['source' => 'EXT:mediaoembed/Resources/Public/Icons/ContentMedia.svg']
);
unset($iconRegistry);