ext_tables.php

<?php

declare(strict_types=1);

use TYPO3\CMS\Core\Imaging\IconProvider\SvgIconProvider;
use TYPO3\CMS\Core\Imaging\IconRegistry;
use TYPO3\CMS\Core\Utility\GeneralUtility;

defined('TYPO3') || die();

$iconRegistry = GeneralUtility::makeInstance(
    IconRegistry::class
);
$iconRegistry->registerIcon(
    'extension-bluesky',
    SvgIconProvider::class,
    ['source' => 'EXT:bluesky/Resources/Public/Icons/Extension.svg']
);