You will find the actualy php supported versions on following link:
https://www.php.net/supported-versions.php
It is recommended to use supported version of php.
Notice that PHP 7.4 an higher does not work with vcruntime140.dll. If you try to use it you get error 500 from IIS.
If you start php in commandline you will get following error:
C:\Program Files (x86)\PHP\v7.4>php
PHP Warning: ‘vcruntime140.dll’ 14.0 is not compatible with this PHP build linked with 14.16 in Unknown on line 0
In that case you have to install the new redistributables
x64 Redistributable for Visual Studio 2015-2019 or
x86 Redistributable for Visual Studio 2015-2019