This is the one missing piece for creating truly responsive layouts. Currently, at least one item in an auto layout component must be set to a fixed pixel width. Either (a) the auto layout children must be set to a px-based width, allowing the gap between items to be set to auto, or (b) the gap between items must be set to a fixed width, allowing the auto layout children to be set to “fill.”
Percentage or fr-based width seems to be the only remaining barrier to responsive designs in Figma. It also seems to render the new min-/max-width feature considerably less useful. Rather than designing fluid layouts, I’m still designing for fixed breakpoints. To take a step back, Figma’s made huge steps forward to help us automate the tedium of designing at different screen sizes (primarily via variable modes), but keeping auto layout dependent on fixed pixel widths seems like a big lacuna.