Is there anything I should do on Generatepress Settings / CSS ? I saw I could change the Page Builder Container layout but then everything become unboxed (like the title of the page for example that is not pushed with Beaver Builder).
Are you using the default Beaver Builder or Beaver Themer?
As far as I understand, if you only want to use page builder for the content part and leave header and footer to GP then you should just use Beaver Builder instead of Themer.
That way you can just use the page builder container – it will only change the content container width.