Images saved from websites are often WebP, which some apps, printers and upload forms reject.
Add your WebP images above, check that JPG is selected, and click Convert images. Each file downloads as JPG; several files come in one ZIP.
Quality is set to 92% by default, which looks the same as the original. You can raise it to 100%.
No. The conversion happens inside your browser, so your photos never leave your phone or computer.