Why does Bootup.php run with PHP 5.4.16 from with Craft script but PHP 7.4.10 from the terminal command line?

This is a problem encountered apparently by a lot of users when installing from the Craft setup/install files from the Craft web site.

PHP Warning: Unsupported declare 'strict_types' in /var/craft/vendor/voku/portable-utf8/src/voku/helper/Bootup.php on li PHP Fatal error: Default value for parameters with a class type hint can only be NULL in /var/craft/vendor/voku/portablec/voku/helper/Bootup.php on line 27 Script @php craft setup/welcome handling the post-create-project-cmd event returned with error code 255

The following scenario yields this error:

• A fresh install of craftcms

• installed with composer

• using these instructions: https://craftcms.com/docs/getting-started-tutorial/install/files.html#what-s-composer

• On a bran new unused DigitalOcean Plesk/Centos7 machine

• with php aliased to the Plesk php 7.4 folder

• With CLI php -v verified as returning 7.4

• With all the required php extensions

• With the web server visited and phpver command verified as returning 7.4

• with composer updated

  # composer depends danielstjules/stringy

  # voku/stringy 6.4.0 replaces danielstjules/stringy (~3.0)

Diagnosing it, Right, putting echo phpversion(); into Bootup.php and running from Bash returns 7.4.

But comment everything in Bootup.php out, put echo phpversion(); into it and run craft, and when it calls Bootup.php, it returns 5.4.16.

Why is this? Why does it run with a different php version when run from within the Craft script, and how is this fixed to run with 7.4?

# Include the location of the PHP 7.4 binary in your path
export PATH=/opt/plesk/php/7.4/bin:$PATH
# Ensure that any calls to composer are run with the PHP 7.4 binary
alias composer='/opt/plesk/php/7.4/bin/php /usr/lib64/plesk-9.0/composer.phar'