bbPress.org

ok, put this in the custom css

.single-post:not(.has-sidebar) #primary, 
.page.page-one-column:not(.twentyseventeen-front-page) #primary, 
.archive.page-one-column:not(.has-sidebar) .page-header,
 .archive.page-one-column:not(.has-sidebar) #primary {
  max-width: 100% !important;
}

you may need to play with it if it affects other parts of your site.

if you don’t know how to do this – come back