get_custom_logo

 * Displays the Site Icon URL.
 *
 * @since 4.3.0
 *
 * @param int    $size    Optional. Size of the site icon. Default 512 (pixels).
 * @param string $url     Optional. Fallback url if no site icon is found. Default empty.
 * @param int    $blog_id Optional. ID of the blog to get the site icon for. Default current blog.
 */
function site_icon_url( $size = 512, $url = '', $blog_id = 0 ) {
	echo esc_url( get_site_icon_url( $size, $url, $blog_id ) );
}

/**
 * Whether the site has a Site Icon.
 *
 * @since 4.3.0
 *
 * @param int $blog_id Optional. ID of the blog in question. Default current blog.
 * @return bool Whether the site has a site icon or not.
 */
function has_site_icon( $blog_id = 0 ) {
	return (bool) get_site_icon_url( 512, '', $blog_id );
}

/**
 * Determines whether the site has a custom logo.
 *
 * @since 4.5.0
 *
 * @param int $blog_id Optional. ID of the blog in question. Default is the ID of the current blog.
 * @return bool Whether the site has a custom logo or not.
 */
function has_custom_logo( $blog_id = 0 ) {
	$switched_blog = false;

	if ( is_multisite() && ! empty( $blog_id ) && get_current_blog_id() !== (int) $blog_id ) {
		switch_to_blog( $blog_id );
		$switched_blog = true;
	}

	$custom_logo_id = get_theme_mod( 'custom_logo' );

	if ( $switched_blog ) {
		restore_current_blog();
	}

	return (bool) $custom_logo_id;
}

/**
 * Returns a custom logo, linked to home unless the theme supports removing the link on the home page.
 *
 * @since 4.5.0
 * @since 5.5.0 Added option to remove the link on the home page with `unlink-homepage-logo` theme support.
 * @since 5.5.1 Disabled lazy-loading by default.
 *
 * @param int $blog_id Optional. ID of the blog in question. Default is the ID of the current blog.
 * @return string Custom logo markup.