JPEG is a practical format for an ordinary photograph when you need a widely usable sharing file. Converting to JPEG makes a new image file with JPEG encoding. Changing a name from .png or .webp to .jpg does not perform that conversion and can confuse the app or person receiving it.
This page starts with JPEG quality at 92%, original dimensions, no crop, sharpening off, and no target size. These are export choices for a first comparison. They do not guarantee a smaller file than the input. A tiny, already optimised source may become larger after conversion, while a detailed PNG photograph may shrink substantially. Inspect the result rather than assuming the extension predicts the file size.
JPEG does not keep transparency. If your source is a logo or cut-out product with transparent areas, check the exported background carefully. Set the intended background in a design editor before conversion when its colour matters. If transparency is required by the recipient, use a suitable PNG or the original file instead of forcing a JPEG. WhatsApp photo messages and Document attachments are separate delivery decisions that you make after downloading.