ext_localconf.php

<?php
defined('TYPO3_MODE') or die();

$boot = function () {
    $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['t3lib/class.t3lib_pagerenderer.php']['render-preProcess']['wsless'] = \WapplerSystems\WsLess\Hooks\RenderPreProcessorHook::class.'->renderPreProcessorProc';

    // Caching the pages - default expire 3600 seconds
    if (!is_array($GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['ws_less'])) {
        $GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['ws_less'] = [
            'frontend' => \TYPO3\CMS\Core\Cache\Frontend\VariableFrontend::class,
            'backend' => \TYPO3\CMS\Core\Cache\Backend\FileBackend::class,
            'options' => [
                'defaultLifetime' => 0,
            ],
        ];
    }
};

$boot();
unset($boot);