Could it be that it doesn't show up due to the theme?

@onurkansan,

This is not an update issue, something wired is going on with your website. The forum was accessible 1 seconds ago, not it's not accessible. You've mixed forum page base URL and it seems you've created multiple pages.

Make sure you have only one page with [wpforo] shortcode in Dashboard > Pages admin page.

Make sure the page slug is the same Board Slug. Board slug can be found in Dashboard > wpForo > Boards > Edit Board admin page.

BTW, why I see the forum here?

https://biansiklopedi.com/kayit-ol/

I solved the problem. I installed one of the old backups and the problem is solved