ext_localconf.php

<?php

if (!defined('TYPO3_MODE')) {
    die ('Access denied.');
}

$extConf = unserialize($_EXTCONF);

// select method of using glossary
switch (strtoupper($extConf['glossaryWHEN'])) {
    // fast: this hook is called with the cached page containing int-script elements for uncached subparts
    case 'BEFORECACHING':
        $TYPO3_CONF_VARS['SC_OPTIONS']['tslib/class.tslib_fe.php']['contentPostProc-all']['tx_a21glossary'] = SveWap\A21glossary\Hooks\FrontendHook::class . '->processHook';
        break;

    // slow: this one is for the final page containing also the uncached areas
    case 'AFTERCACHING':
        $TYPO3_CONF_VARS['SC_OPTIONS']['tslib/class.tslib_fe.php']['contentPostProc-output']['tx_a21glossary'] = SveWap\A21glossary\Hooks\FrontendHook::class . '->processHook';
        break;

    // off: do not invoke the glossary engine automatically
    default:
    case 'OFF';
        break;
}

unset($extConf);

TYPO3\CMS\Extbase\Utility\ExtensionUtility::configurePlugin('SveWap.A21glossary', 'Pi1', [
    'Glossary' => 'index,search'
], [
    'Glossary' => 'search'
]);