I find a work around by using Elementor.

For the community:

I add a new "Section," then I insert 3 "Columns," then I insert my widget, "Forums," "Recent topics," and "recent posts."

It covers the width of the page

Thanks, Chris for your support

if the result is very bad, it's not the solution :-) Any nice other solution?

For information, I am using Elementor, but I can use the default WordPress editor, too.

What are the files used for the widget? PHP and CSS

Thanks

That's possible to do with Flexbox, but the design would be very bad, you won't get what you were looking for, ass the HTML isn't written for using Flexbox.

I am using wpForo wirdget for my wordpress site. By default forums are ranked in 1 column.

How can I have set my forums on 3 columns, like screenshot attached?

Thanks