Hallo zusammen,
mit dem kleinen Code am Ende der localconf.php einreihen, sofern man RealURL da eingebunden hat.
Danach nur noch die Root-ID angeben und schon sollte das passen 😉

/**      domain1.tld    */
// default Konfiguration übernehmen
$TYPO3_CONF_VARS['EXTCONF'] ['realurl'] ['domain1.tld'] =
$TYPO3_CONF_VARS['EXTCONF'] ['realurl'] ['www.domain1.tld'] = $TYPO3_CONF_VARS['EXTCONF'] ['realurl'] ['_DEFAULT'];

// Rootpage ID anpassen
$TYPO3_CONF_VARS['EXTCONF'] ['realurl'] ['domain1.tld'] ['pagePath'] ['rootpage_id'] =
$TYPO3_CONF_VARS['EXTCONF'] ['realurl'] ['www.domain1.tld'] ['pagePath'] ['rootpage_id'] = '1';


/**      domain2.tld    */
// default Konfiguration übernehmen
$TYPO3_CONF_VARS['EXTCONF'] ['realurl'] ['domain2.tld'] =
$TYPO3_CONF_VARS['EXTCONF'] ['realurl'] ['www.domain2.tld'] = $TYPO3_CONF_VARS['EXTCONF'] ['realurl'] ['_DEFAULT'];

// Rootpage ID anpassen
$TYPO3_CONF_VARS['EXTCONF'] ['realurl'] ['domain2.tld'] ['pagePath'] ['rootpage_id'] =
$TYPO3_CONF_VARS['EXTCONF'] ['realurl'] ['www.domain2.tld'] ['pagePath'] ['rootpage_id'] = '2';

Liebe Grüße
Marc