Hello Mert,
Thank you for your message.
I had the same problem as reported above, i.e. 'news' posted to the site news forum was not being emailed out to site users.
The solution, as you suggest, is:
- Before creating the site forum: got to Site Admin > Front Page settings > Default front page role = Student
- Create the Site News forum by turning on the "Latest News" block and click on "Add a new topic"
The site news forum should then be set up with all site users automatically subscribed.