Not sure if this helps you but I’ve noticed our implementation’s source set contains a different transform URL for each size, see example below, only problem is if the original image resolution is lower than any of those formats then the output is fixed to the lowest resolution.
srcset="https://assets.kmart.com.au/transform/83759511-ab34-4111-998a-d45e4edf2a92/43620890-1?io=transform:fit,width:640,height:640&quality=90 640w, https://assets.kmart.com.au/transform/83759511-ab34-4111-998a-d45e4edf2a92/43620890-1?io=transform:fit,width:750,height:750&quality=90 750w, https://assets.kmart.com.au/transform/83759511-ab34-4111-998a-d45e4edf2a92/43620890-1?io=transform:fit,width:828,height:828&quality=90 828w, https://assets.kmart.com.au/transform/83759511-ab34-4111-998a-d45e4edf2a92/43620890-1?io=transform:fit,width:1080,height:1080&quality=90 1080w, https://assets.kmart.com.au/transform/83759511-ab34-4111-998a-d45e4edf2a92/43620890-1?io=transform:fit,width:1200,height:1200&quality=90 1200w, https://assets.kmart.com.au/transform/83759511-ab34-4111-998a-d45e4edf2a92/43620890-1?io=transform:fit,width:1920,height:1920&quality=90 1920w, https://assets.kmart.com.au/transform/83759511-ab34-4111-998a-d45e4edf2a92/43620890-1?io=transform:fit,width:2048,height:2048&quality=90 2048w"