> I built WebPtoPNG after getting frustrated with converters that throttle uploads or phone data

Why would you want to do it in a browser anyway? Just run it local. There are many open source image editors and converters to choose from.

ImageMagick is one: https://imagemagick.org/

GIMP is another: https://www.gimp.org/

Krita is another: https://krita.org/en/