Responsive Image srcset not complete

Hello Cumminity! ??

My name is Philipp and i’m a (still learning) web-developer.

Currently i’m working with WP and Timber. As i stumbled upon responsive images i couldn’t simply ignore to add my custom image sizes to WP.

As i did so via add_image_size, “Regenerate Thumbnails” obviously noticed my new image size and re-generated the media.

Code to add image size:

if(function_exists('add_image_size')) {
add_image_size( 'slider-cropped', 500, 500, true );
}

This one is triggered with the ‘after_theme_setup’-hook and the function is called after the ‘add_theme_support(‘post_thumbnails’)’-function.

I am working with srcsets, thus i expected my new image src to be appended to my srcset automatically. This actually is not what’s happening.
As i call my images srcset in my template, only WP standard sizes are shown.
I’m returning image-arrays from an ACF-Gallery-field.

As i call the new image size by name,
‘{{Image(img).src(‘slider-cropped’)}}’
respectively, the image is shown. Nevertheless i want WP to add it automatically to my srcset.

I’d appreciate any help, i’m stuck here for a long long time and read like all posts anywhere on this topic.

Thanks in advance,
Philipp