Refresh Theme Banner image behavior

Store Design
8

Go to the Online Store - Theme - three dots - and search the .css extension file, it could be custom.css / base.css or something like this.
Then paste this inside, on the bottom:

@media screen and (max-width: 640px) {
#Banner-template--15474553880710__image_banner_gmRjWx .media > img {
  object-fit: contain !important;
}
}

max-width is your maximum screen width where these styles should be added.