Ok, I found a workaround. With css I set horizontal images takes 2 columns so the aspect ratios are similar to original images (not the exact same). Just add some text in image alt section, I use "hr". Then, you have to play with columns number to make slide working correctly.
In these example my images are 3:2 and 2:3.
Here the code and image example:
li:has(img[alt~="hr"]) {
grid-column-start: 1 !important;
grid-column-end: 3 !important;
}
.user-items-list-carousel__slides li, .user-items-list-carousel__media-container, .user-items-list-carousel__media-inner, .user-items-list-carousel__slides img {
height:100% !important;
object-fit:cover;
border-radius:20px; //use this if you want round corners
}
