Open a downloaded WebP in a program that refuses it.
This file stays on your device
Drop files here
Up to 30.0 MB
PNG is lossless, so quality does nothing here.
This is the most common reason anybody converts anything. A picture saved from a website arrives as WebP, and then a document editor, an older photo tool, or a printing service will not take it. PNG is read by everything, and it keeps the clear background that WebP files often have.
The file gets larger, sometimes several times larger. Nothing else changes: the picture is stored exactly as it arrived.
If the picture is a photograph and the size matters more than the transparency, convert it to JPG instead. It will be far smaller and no program will refuse it either.