Thumbnail image is not cropped to the correct size

I noticed that this theme does not crop images to create thumbnails. Instead, it simply uses CSS to shrink the original image and display it to the user.

This means that the browser still has to download the original large-sized image to the user’s computer. This results in Google PageSpeed Insights giving the website a lower loading speed score.

The image I attached clearly shows this:

The original image size is 1024×534 pixels.
However, the actual thumbnail size needed is only 80×72 pixels.
I have tried to find any customizations to get Viral Mag to crop and use the correct-sized thumbnail, but I have not found any.

Is there any customization in the functions.php file that can do this?

Thank you.

https://mpthoidai.com/wp-content/uploads/2023/08/thumbnail_mpthoidai.jpeg