how to install CI4 in sub folder in shared hosting?

Finally i found a simple solution:
1- create index.php in the ci4 root folder that contain ( include 'public/index.php' )
2- then copy public/.htaccess to the root folder

You do not absolutely need a directory named "public". You can reorganize the directories like you want. You just need to have a public and a private directory. 

You can put all the content of the "public" directory anywhere you want, with the name you want, and then set the path for the private directory in index.php :

Code:

// Location of the Paths config file.
// This is the line that might need to be changed, depending on your folder structure.
$pathsPath = FCPATH . '../my-ci4-webapp/app/Config/Paths.php';
// ^^^ Change this if you move your application folder