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It would be possible to find a local developer to help you with that custom code. They can add new form elements using something like bp_docs_closing_meta_box hook and disable the activity item by doing something like

add_action( 'bp_docs_doc_saved', 'dc_maybe_do_not_create_activity_item', 8 );
function dc_maybe_do_not_create_activity_item() {
	// Watch for your custom form element
	$condition_is_set = $_REQUEST['make_no_activity_item'] ?? false;
	if ( $condition_is_set ) {
		remove_action( 'bp_docs_doc_saved', 'bp_docs_post_activity' );
	}
}