Hi Gert B,
Welcome to Affinity Forums
There's a few different methods (and parameters) to generate/write JPG files (this also applies to other formats) thus exporting the file as JPG even at 100% quality (it still compressed despite the 100% value) may lead to increased sizes depending on the method used to originally generate/save the file. Additionally Affinity apps currently don't perform any image optimisations on export - we hope to improve this later. If you are looking to get the best possible quality/size ratio now I advise you to export the file to a non-compressed format (PNG, TIFF etc) and then use a third party image optimiser to reduce their file size - they usually offer quite a few options to generate/optimise the files. Take a look at these for example: ImageOptim (Mac), JPGmini (Mac and Windows), Optimage (Mac), RIOT (Win) etc (some are free).
Do you mind uploading the original JPG using this link for us to take a look if there's something else going on please? Thanks.
