When switching to PHP 8.0.21 this happens:
AH01071: Got error 'PHP message: PHP Fatal error: Uncaught TypeError: in_array(): Argument #2 ($haystack) must be of type array, string given in /var/www/vhosts/egf.de/httpdocs/wp-content/plugins/ajax-search-pro/includes/classes/Hooks/Actions/IndexTable.php:150\nStack trace:\n#0 /var/www/vhosts/egf.de/httpdocs/wp-content/plugins/ajax-search-pro/includes/classes/Hooks/Actions/IndexTable.php(150): in_array()\n#1 /var/www/vhosts/egf.de/httpdocs/wp-content/plugins/ajax-search-pro/includes/classes/Hooks/ActionsManager.php(226): WPDRMS\\ASP\\Hooks\\Actions\\IndexTable->cron_extend()\n#2 /var/www/vhosts/egf.de/httpdocs/wp-content/plugins/ajax-search-pro/includes/classes/Hooks/ActionsManager.php(165): WPDRMS\\ASP\\Hooks\\ActionsManager::registerCron()\n#3 /var/www/vhosts/egf.de/httpdocs/wp-content/plugins/ajax-search-pro/includes/classes/Core/Manager.php(344): WPDRMS\\ASP\\Hooks\\ActionsManager::registerAll()\n#4 /var/www/vhosts/egf.de/httpdocs/wp-content/plugins/ajax-search-pro/includes/classes/Core/Manager.php(75): WPDRMS\\ASP\\Core\\Manager->loadH...', referer: https://www.egf.de/wp-admin/options-general.php?page=updraftplus&tab=backups