I do not understand what that would be good for.
Just create the site, export its registry key and import it to the target environment.

Though we do not recommend using stored site in scripting anyway. It leads to maintenance problems eventually.
https://winscp.net/eng/docs/scripting#configuration

No, that solution is to open a session and send files.

I need a script to create the credentials of a site and store them in Registry like the GUI does. (see attached image)

Then when I call that script on a schedule task (running with SYSTEM account), I don't need to pass the user/password, but only the site info (app/app)

Are you looking for this?
https://winscp.net/eng/docs/ui_generateurl#script

I'm automating a manual deployment plan
one of the steps prior to run the following bat script is to create app/app1 site credentials
the script uses app/app1 login that currently is created in WinSCP ui.

My question is can this login be created via commandline?

attached is the login window info with the info that needs to be scripted to be used on my automation

Script:
cd C:\Program Files (x86)\WinSCP
WinSCP.com app/app1 /log="C:\temp\logs_%DATE:/=-%.txt" /command "put -filemask=* H:\EXTRACT\TRANSFER\* -delete" "close" "exit"

I'm not sure I understand your question.

But maybe you want to read this:
https://winscp.net/eng/docs/guide_automation

Hi all, I'm trying to add a login to winscp via command prompt. But I'm unable to find an waay to do it? it is possible, or sites/user info can only be added in UI Login window?

I need to have it stored to avoid to have the user and password stored in my batch file (I'm building a schedule task to send files every day)

Thanks