RyuZU said:
JPG doesn't support transparency, must be saved in PNG to maintain transparency.
You saved in JPG, look if there is how to save in PNG in the program.
I saved it in PNG. I think my phone changed it to JPG.

RyuZU said:
It's easy to recognize, this image one part of it has artifacts and the other not, download this image and zoom in on both parts, it is easier to compare, and to remove use waifu2x, I use desktop version, and sometimes this site, use the site, should work on mobile, on noise reduction "low" is enough.
Should i delete GIMP then?