Found it, simple fix, can anybody test?
In the file popup-maker/includes/pum-condition-functions.php replace lines 74-93 with:
$templates = wp_get_theme()->get_page_templates();
if ( $name == 'page' && ! empty( $templates ) ) {
$conditions[ $name . '_template' ] = array(
'group' => $post_type->labels->name,
'name' => sprintf( _x( '%s: With Template', 'condition: post type plural label ie. Pages: With Template', 'popup-maker' ), $post_type->labels->name ),
'fields' => array(
'selected' => array(
'type' => 'select',
'select2' => true,
'multiple' => true,
'as_array' => true,
'options' => array_flip(
array_merge(
array( 'default' => __( 'Default', 'popup-maker' ) ),
$templates
)
),
),
),
'callback' => array( 'PUM_Condition_Callbacks', 'post_type' ),
);
}