PNG is the right target when a HEIC needs to go into a design tool, a document or a workflow that must not add compression artefacts, or when the image has transparency you want to keep. PNG stores every pixel exactly, so nothing more is lost after the HEIC is decoded. The cost is size: a 12-megapixel photo as PNG is commonly 15 to 25 MB, many times the HEIC. If you only need the photo to open everywhere, JPG is the smaller choice.
The defaults suit most files. Under Options you can resize the result.
Most browsers other than Safari cannot read HEIC themselves, so a HEIC decoder of under 1 MB is downloaded the first time and kept in the browser cache. Camera metadata such as EXIF and GPS location is not copied into the PNG, and the photo's rotation is applied so it stays upright.