Just to amplify LazyOne's comment:
At least in my case it was missing because since version 2021.1 of PHPStorm PHP is not located under the "Languages and Frameworks" anymore. Instead it sits at the very top of the settings:
So, you mean to highlight all pieces of code that will not work with the PHP version you are writing it in, right? That can be done here:
Preferences -> Languages & Frameworks > PHP
and the same on Mac:
PhpStorm -> Preferences (⌘,) -> Languages & Frameworks > PHP
Or with newer versions of PhpStorm in Windows:
File -> Settings -> Languages & Frameworks > PHP
then select your PHP version, for example, 7.0
This is very useful when your local system runs PHP 7.0, for example, but production is running PHP 5.5.
That way PhpStorm will warn you which parts will not work in production, show proper hints during writing code according to the selected version, etc.
In case your field is disabled.
Probably your settings "Synchronize IDE settings with composer.json" is enabled
You may change your PHP version in composer.json file
"require": {
"php": ">=7.1.0",
}
OR disable your settings in this path
File -> Settings -> Languages & Frameworks > PHP > Composer
*If you change your composer.json file - As Félix Gagnon-Grenier commented, Keep in mind it has effects on the way packages will be required later
My version of PHPStorm is 2018.3.6
Upgrade your IDE to a newer version. PHP 7.4 support was added later (initial support in 2019.2 and proper one in 2019.3: https://www.jetbrains.com/phpstorm/whatsnew/2019-3/).
P.S. Latest PhpStorm is 2021.1.1 and it supports PHP 8.0
https://www.jetbrains.com/phpstorm/whatsnew/
You need to update to new version of PHP Storm.
The current version that I'm using is:
PhpStorm 2020.2 Build #PS-202.6397.115, built on July 29, 2020
and supports version 7.4 and latest 8.0 for PHP Language Level pack.