Hi I got version 

PHP 7.3.15 (cli) (built: Feb 24 2020 22:30:19) ( NTS ) Copyright (c) 1997-2018 The PHP Group Zend Engine v3.3.15, Copyright (c) 1998-2018 Zend Technologies
/home>apt-get install php7.4-pdo php7.4-mysql

And this is PaaS so it have pre define and I cannot install 7.4, but Magento 2.3.5 is compatible with 7.3 if I'm correct