There is no way to lock the responsive aspect ratio of a shape or image. This is a really common requirement but really limits the effectiveness of responsive designs.
E.g. I have a 1:1 aspect ratio image on mobile, I want that image to be 1:1 on tablet. Right now this is not supported responsive behavior. Design file example / explanation here: https://www.figma.com/design/qW44TD0IYhiXzaaioioSe3/Repsonsive-image?node-id=0-1&t=zYHwDKI9qSR3KVpY-1
