Susan M. You could try using :nth-child() to target the image inside of every x number of items to style them however you see fit.
This snippet
<style>
.portfolio12_item:nth-child(2n) .portfolio12_image1 {
aspect-ratio: 1 / 1;
}
</style>
Creates this layout (see image) in a collection list.
In this instance using 2n creates a fairly grid like layout because all the content is the same, but using 5n or anything else still looks like a masonry layout.