Edge quality goes down when exporting with Gimp (no compression, any format)

Question

This image looks pretty in Gimp’s native XCF format:

:

After exporting to any internet format without compression it looks like this:

What’s the reason for this loss of quality, and how can I avoid it?

Answer 1

Any format, really? WebP? JPG?

For GIF and color-indexed PNG (is the image color-indexed?), the opacity is "binary" (fully transparent or fully opaque), so edge pixels cannot assume the partial opacity that makes things look smooth.

Otherwise, please upload the PNG to a place where it won't be altered before we can download it.