add_filter( 'frm_section_is_open', '__return_true' );

add_filter( 'frm_section_is_open', 'open_section_for_target_field', 10, 2 );
function open_section_for_target_field( $open, $field ) {
	$target_section_id = 18635; //Replace 18635 with the section field ID
	$id                = is_object( $field ) ? $field->id : $field['id'];
	if ( (int) $id === $target_section_id ) {
		$open = true;
	}
	return $open;
}

add_filter( 'frm_section_is_open', 'open_section_for_target_form', 10, 2 );
function open_section_for_target_form( $open, $field ) {
	$form_id        = is_object( $field ) ? $field->form_id : $field['form_id'];
	$target_form_id = 1012; //Replace 1012  with your form ID
	if ( (int) $form_id === $target_form_id ) {
		$open = true;
	}
	return $open;
}