TYPO3 Core

I can confirm this bug with the same TYPO3 and PHP version.

\TYPO3\CMS\Frontend\Controller\TypoScriptFrontendController::$tmpl is possibly null in \TYPO3\CMS\Frontend\Controller\TypoScriptFrontendController::checkTranslatedShortcut().

I can confirm this bug in 11.5.30.

The cause of error lies here in the "\TYPO3\CMS\Frontend\Controller\TypoScriptFrontendController"

    protected function checkTranslatedShortcut(int $languageId, ServerRequestInterface $request)
    {
        if (!is_null($this->originalShortcutPage)) {
            $originalShortcutPageOverlay = $this->sys_page->getPageOverlay($this->originalShortcutPage['uid'], $languageId);
            if (!empty($originalShortcutPageOverlay['shortcut']) && $originalShortcutPageOverlay['shortcut'] != $this->id) {
                // the translation of the original shortcut page has a different shortcut target!
                // set the correct page and id
                $shortcut = $this->sys_page->resolveShortcutPage($originalShortcutPageOverlay, true);
                $this->id = ($this->contentPid = $shortcut['uid']);
                $this->page = $this->sys_page->getPage($this->id);
                // Fix various effects on things like menus f.e.
                $this->fetch_the_id($request);
                $this->tmpl->rootLine = array_reverse($this->rootLine);
            }
        }
    }

"$this->tmpl->rootLine = array_reverse($this->rootLine);" fails due to "$this->tmpl" being null.

Same here.
TYPO3 11.5.33
PHP 8.2

Not a real fix, but I avoided the error like this:

if (!is_null($this->tmpl)) {
    $this->tmpl->rootLine = array_reverse($this->rootLine);
}

This looks still present on TYPO3 11.5.39 but resolved on 12 and 13 (latest main)