What PNG gives you, and what it does not
PNG stores every pixel exactly, so editing and saving the picture again loses nothing more. It does not bring back detail that JPG compression already removed, and the PNG is usually several times larger than the JPG it came from: the sizes before and after show by how much.
A see-through background
A JPG has no transparency, so its PNG keeps the same background. To make a plain background see-through, use the background remover on the PNG afterwards.
The new files are made in your browser from your images. Nothing is uploaded, and location and camera details (EXIF) are left out.