WebP is common on websites and in messengers. If an editor, printer, or Windows form only opens JPG — re-encode the file here.
Decoding and JPEG saving run in the browser: the source is never uploaded. You can cap the long edge so the attachment doesn’t balloon.
Batch: several WebP at once, then ZIP or Share on iPhone. Use the quality slider when you need a sharpness-vs-size tradeoff.