SIZE THUMBNAIL NOT SEO FRIENDLY

Hi,

I use the Stackable posts block with the ‘miniature” image size displaying my last messages. But it’s not the thumbnail that is used but the original image resized in HTML…
For the SEO, serving appropriately-sized images can save many bytes of data and improve the performance of the webpage, especially on low-powered (eg. mobile) devices.

<figure class="ugb-blog-posts__featured-image ugb--shadow-3"><a href="https://www.mywebsite.fr/blog/category/myPost/"><img src="https://cdn.mywebsite.fr/wp-content/uploads/MyImage-1024x683.jpg" alt="" width="357" height="238"></a></figure>

It’s possible to fix this?
Thank You