How to get an upscaled png from Google AI Studio or Gemini Pro

Hi All, I put my API key into Google AI Studio and chose Nano Banana Pro, then requested upscaling using a prompt of:
Upscale this image to 4096 wide by 2730 high. Produce a png. Do not modify the picture other wise.

It produced a JPG instead.

In Gemini, chat it produced a PNG but did not upscale.

What am I doing wrong?