Two rules matter for printing. First, the format: JPG is the only one universally accepted by kiosks and labs, which is why the converter above is locked to it at 95% quality — visually lossless, safely inside every service's requirements. Second, the resolution: leave the max-width field empty. Print needs every pixel you have (a 10×15 cm print uses about 1800×1200 at 300 dpi; larger formats need more), so never downsize photos destined for paper.
iPhone photos in HEIC and web images in WebP are the two usual offenders — drop either above. If a lab asks for « sRGB JPG », that's exactly what your browser produces here.