This tool reads your HEIC image directly in the browser and encodes a PNG copy, so there is no upload, no queue and no waiting for a server. It works on desktop and mobile.
iPhone photos in HEIC will not open in many Windows programs and websites. PNG is lossless and universally supported, which makes it a safe archive format.
PNG versions of photos are much larger than HEIC or JPG. For sharing, use the HEIC to JPG converter instead.