How Do I Prevent An Image From Automatically Adjusting In Guttenberg Block Gallery?

Question

Gutenberg is applying a flex-grow: 1; to the items, which allow it to fill the space. You override this by pasting the following into your css.

.blocks-gallery-grid .blocks-gallery-image, 
.blocks-gallery-grid .blocks-gallery-item, 
.wp-block-gallery .blocks-gallery-image, 
.wp-block-gallery .blocks-gallery-item {
   flex-grow: 0;
}

Ideally, you do this in your theme, but if you urgently need this up, or if you are unfamiliar with WordPress development, then you can add this to your customizer “Additional CSS” tab.