To change product gallery from Stacked to Slideshow on Mobile, you can follow these.
#1. First, edit a Product

Next, click Edit Section

#2. Choose Slideshow (we will use code to change it to Stacked on Desktop)

#3. Next, use this code to Custom CSS to change Slideshow to Stacked on Desktop.
/* Stacked Product */
@media screen and (min-width:768px) {
.ProductItem-gallery-slides-item {
position: static !important;
height: auto !important;
visibility: visible !important;
opacity: 1 !important;
margin-bottom: 20px;
}
.ProductItem-gallery-slides:before {
padding: 0 !important;
}
.ProductItem-gallery-scroll {
display: none !important;
}
.ProductItem-gallery-carousel-controls {
display: none !important;
}}

#4. If you want to do this for a specific product only, you can edit Additional Info > Add a Code Block
Click plus icon to add a Code Block


and paste this code into Code Block
<style>
/* Stacked Product */
@media screen and (min-width:768px) {
.ProductItem-gallery-slides-item {
position: static !important;
height: auto !important;
visibility: visible !important;
opacity: 1 !important;
margin-bottom: 20px;
}
.ProductItem-gallery-slides:before {
padding: 0 !important;
}
.ProductItem-gallery-scroll {
display: none !important;
}
.ProductItem-gallery-carousel-controls {
display: none !important;
}}
</style>
