Display folder from ID

Sure, you can use a loop like bp_docs_has_docs( array( 'folder_id' => {folder_to_display} ) ); See https://github.com/boonebgorges/buddypress-docs/blob/master/includes/templates/docs/docs-loop.php#L113 for an example you could cadge.

Or you could add the query parameter to your directory page’s url, like https://mysite.com/docs/?folder={folder_to_display}

Thanks for your help, that’s great.