As in the title, we should be able to control how much JPEG images get compressed when exporting a layout to PDF file.
To be clear: I mean compression, not downsampling. JPEG compression will lower the size of the output file if it contains raster images, but it doesn't change their resolution. Downsampling will lower their resolution. I only talk about compression here.
So when we put JPEG images to a layout and export the layout to PDF, we get medium-degree compression of those images, and we cannot change it. It's just not possible to output a high quality JPEG in a PDF sheet. Yes, we could import PNG/TIFF images with lossless compression and ArchiCAD will retain it but we don't have any control over lossy compression that JPEGs use.
My suggestion is to create a setting that would control the level of lossy compression - just like pretty much any other program for making design layouts and saving them to PDF.
I am happy to say we took notice of this wish and I have added it to our Wish List database (please refer to it as Wish #13059). Hopefully, our Product Management team will adopt this one in the future.