(1) Photopea supports ALL PNG images. It can export palletted PNGs with 8 bit alpha (which PS can not for some reason).
(2) Custom Shape tool can do it in Photopea.
(3) Photopea can load APNG (or GIF) and save it back to APNG (or GIF). I.e. you can use PP for editing animations. See more here: https://www.photopea.com/learn/animations