PHP Fatal Error with PHP 7.4

[23-Jun-2020 23:21:35] WARNING: [pool gesandtschaft.org] child 14725 said into stderr:

"NOTICE: PHP message: PHP Fatal error: Uncaught TypeError: Argument 2 passed to phpbb\template\context::assign_block_vars() must be of the type array, string given, called in /var/www/vhosts/gesandtschaft.org/httpdocs/phpbb/template/context.php on line 252 and defined in /var/www/vhosts/gesandtschaft.org/httpdocs/phpbb/template/context.php:190"