Under Look and feel > Desktop > Screen saver > Banners and pictures there is an option called "slide show." On my previous KDE system, that works perfectly. But now that I've installed a new Linux system with the most recent KDE, I cannot find any way to specify a folder within my home filesystem to use as the source of images for the slide show, as I was able to do before. What do I need to do to get the screen-saver slide-show to work with a folder of images that I specify?

Open the Screensaver panel, then select Banners & Pictures > Slide Show. Then press "Setup".

I did try "setup" before and it did not work -- did not open to a dialog that allowed choosing a folder. But trying it again today did work, so all is well. Thank you.

run xscreensaver-demo to set slide show directory.