kirki: CSS output doesn't work in Kirki 4 (worked perfectly in Kirki 3)

I am using Kirki Customizer typography settings with ‘output’ to automatically assign the CSS. It worked perfectly with Kirki 3 but doesn’t work anymore with Kirki 4 beta as well as today’s 4.0.3 stable release:

Kirki::add_field($mydesignTheme, [
    'type' => 'typography',
    'settings' => 'typography_h1_settings',
    'label' => esc_html__('Advanced Typography', 'mydesign'),
    'description'    => esc_html__('Typo settings description', 'mydesign'),
    'section' => 'advanced_typography_h1',
    'default' => [
        'font-family'    => 'inherit',
        'variant'        => '700',
        'font-size'      => '',
        'line-height'    => '',
        'letter-spacing' => '0',
        'color'          => '#111111',
        'text-transform' => 'none',
        'text-align'     => 'inherit',
    ],
    'priority' => 10,
    'transport' => 'auto',
    'output' => [
        [
            'element' => 'body.single h1, body.blog h1',
        ],
    ],
]);