HEIC is commonly used to store photos efficiently on Apple devices. It can preserve good image quality at smaller file sizes than older formats in many cases, but software support varies. Converting to JPG is useful when a website, editor or older Windows workflow does not accept HEIC.
Practical advice
Use the original source file or URL whenever possible, keep a backup before conversion, and treat browser error messages as troubleshooting signals rather than proof of a specific server-side configuration.