This is how I got it working on one recent site. I had to use the “render” callback function to iterate through the loop and use sage (9) template function. I hope it helps you figure it out!
// Add support for Jetpack's Infinite Scroll
add_theme_support('infinite-scroll', [
'container' => 'main',
'footer' => false,
'type' => 'scroll',
'wrapper' => false,
'posts_per_page' => 12,
'render' => __NAMESPACE__ . '\\infinite_scroll',
]);
function infinite_scroll()
{
echo '<div class="container-inner">';
while (have_posts()) : the_post();
echo template('partials.content-' . get_post_type());
endwhile;
echo '</div>';
}