I have trouble opening a directory within the inappbrowser
What kind of trouble? Do you receive an error message or an unexpected result? Is it just one specific directory that you can't open?
Does it happen with all your test devices on all OS platforms, or is it a specific thing for one device/OS(version)?
...to post a photo on a website for example,
What code does that 'website' use to 'open a directory'? And is the problem 'opening a directory', or rather 'selecting a file' or even 'posting a selected file'?
Wouldn't it perhaps be better to have the user open the 'website' in a regular browser? Do you actually need an app for that website to display?
...believe it is allowed
What is your reason to believe so?
the app have only 2 installed plugins ( inappbrowser and whistelist )
The whitelist only comes into play if you use the inappbrowser plugin to display the website in the webview ('_self'), not if it is displayed in the inappbrowser window.
However, if you are trying to open that directory using some inline script, your CSP might prevent it from being executed.
BTW: are you sure you don't need other plugins, like the splashscreen plugin and the statusbar plugin?