Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 7.4.0". code example

Example 1: Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 7.3.0".

composer install --ignore-platform-reqs

Example 2: Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 7.3.0".

#add to composer.json > config
"platform-check": false,

composer autoload-dump

Example 3: Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 7.3.0".

composer install --ignore-platform-reqs

or 
 #add to composer.json > config
"platform-check": false,

composer autoload-dump