iPhones have saved photos as HEIC since iOS 11 because it halves the storage a photo needs. The trouble starts when the photo leaves the phone: Windows without the HEIF extension, most browsers, many print kiosks and a long list of upload forms reject it. JPG (the same thing as JPEG) is the format all of them accept. Expect the JPG to be larger than the HEIC, often about double, because JPG's 1992 compression is less efficient. A Live Photo's motion is stored by iOS as a separate video, so a HEIC file only ever contains the still.
JPG has no transparency, so see-through areas of a HEIC are filled with a solid colour, white by default; you can change it under Options. The defaults suit most files. Under Options you can set the quality, aim for a target file size and 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 JPG, and the photo's rotation is applied so it stays upright.