How to get user password before being encrypted outside the wordpress core once add a new user from dashboard?

You could create users manually using wp_create_user() function: https://developer.wordpress.org/reference/functions/wp_create_user/

This would allow you to determine the password – but of course, you would have to be careful about how you share that with your other apps.

The other option is to share the public information ( email, username etc ) and then to return and update the password using wp_set_password(): https://developer.wordpress.org/reference/functions/wp_set_password/