Change WebP files to JPG for email, uploads and older software. JPG opens almost everywhere.
PNG ignores the quality setting because it is lossless. Enhance uses smooth upscaling and sharpening, not AI, so it makes soft images crisper but can't recover detail that isn't there. If your browser can't write AVIF, that option reports an error and you can pick another format.
JPG has no transparency, so transparent areas are filled with the background color you choose in the settings.
They are filled with the background color setting, white by default.
85% is a safe balance. Use 92% or more for photos you plan to edit.