Thanks Tutrix but it doesn't solve the issue, because the title is not the case. See:

@piki Changing the slug in an OLD site, will destroy your forum indexing and seo. If it is a new one (or relatively new) it is JUST ok. What do you ...

<!-- Page supported by LiteSpeed Cache 5.3.3 on 2023-04-01 08:54:01 -->

Delete the /community/ page. Check the Shortcode in /forum/ page. Maybe it is not posted correctly.

Then i can only guess that some PLUGIN is doing that. Disable one by one and see from where the issue come.

@wacha When i click and then the 1st forum, i get AGAIN /forum and a 404. Did you manually move the wpForo db in this test site?

@wacha YES. The FORUM URL IS COMMUNITY AND NOT FORUM. Did you bother to check /community ? It is all in there. Please take the time to understand ...

Because the forum is HERE: and not at /forum/

@tarikbayar White Page COULD be a white screen of DEATH, a fatal PHP error. Enable STANDARD Wordpress debug and see if debug.log shows any errors. ...

Remove this <!-- Cached by WP-Optimize (gzip) -- Last modified: Thu, 30 Mar 2023 16:47:52 GMT --> and see if the problem goes away.

Checking other topics, for example It is distorted, showing <blockquote> code from twitter for example.....

Also i would suggest to use a better theme than the default, Kadence for example or whatever you want.

Ok, when visiting that link, press F12 and see several issues, errors, crashes, in your BROWSER console. Fix them and try again.  2023-03...

Install Classic Widgets plugin and try again.