Regarding Featured image Size

Hi there,

go to Customizer > Layout > Blog --> Featured Images, on the Archive tab, leave the width as is, and delete the value from the height.

Thanks, it worked.

Also one more question, can I show different sizes of thumbnail images on different devices.

The example added. Please let me know

Hi there,

Based on the current structure, this CSS should work for most part of what you want:

@media (min-width: 769px) {
     .archive .inside-article, .blog .inside-article {
        display: flex;
        flex-wrap: wrap;
    }
     .archive header.entry-header, .blog header.entry-header {
        width: 100%;
    }
     .archive .post-image, .blog .post-image {
        width: 50%;
    }
     .archive .entry-summary, .blog .entry-summary {
        width: calc(50% - 36px);
    }
}

But if you want to achieve the exact look of your screenshot, it's better to build a content template using a block element:
https://docs.generatepress.com/article/block-element-content-template/

Thanks it's worked

You are welcome :)