Thanks, I’ve improved your code via chatgpt, you should have used that one.
Thanks for your help

.wp-block-gallery.has-nested-images.columns-default figure.wp-block-image:not(#individual-image) {
width: calc(21.33% – var(–wp–style–unstable-gallery-gap, 16px) * 0.66667) !important;
flex: 0 0 20% !important;
}

.wp-block-gallery.has-nested-images.columns-default figure.wp-block-image:not(#individual-image) img {
width: 100%;
height: auto;
object-fit: contain; /
}