When I go to Preferences > Languages & Frameworks > PHP
:
There is no PHP 7.4 in "PHP language level", and the latest is PHP 7.3.
My version of PhpStorm is 2018.3.6
So how to debug why I don't see PHP 7.4? Or simply how to set PHP 7.4?
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