thumbnails of images on the phone larger than on the desktop

Well thats beaten me - i can't see why Google would still be requesting images that are not present in the HTML.

I would suggest removing the filter and look at optimizing your images - they are quite large, for their purpose. Reducing their file size will actually improve real performance whereas as fixing that opportunity will not.

Thanks for the help in any way.
I just didn't understand what you meant by "removing the filter" I don't know how I could reduce the images even more. I have already converted all of them to webp with the "WebP Express" plugin, other attempts that I had to reduce the size the quality decreased noticeably.

Removing the filter - i mean remove the code i provided here:

https://generatepress.com/forums/topic/thumbnails-of-images-on-the-phone-larger-than-on-the-desktop/#post-1498218