When accessing the admin/reports/status page, the PHP version displayed is not the one selected in your Cloud UI, e.g. you can see PHP 7.1 on this page
... whereas the version PHP 7.3 is selected on your Cloud UI as you can see on admin/reports/status/php
This might be caused by some contrib module(s) requiring a specific version of PHP, e.g. the Trailing Slash module (at least until the version 8.x-1.0) which contains in its .module file the following
define('TRAILING_SLASH_MINIMUM_PHP', '7.1');