At the present time, iScreensaver Designer 5.2 provides support for macOS 10.13 High Sierra, but there are some functional limitations.
Please read the 10.13 High Sierra Tech Note
as well as the Release Notes
Due to changes made by Apple, iScreensaver Designer version 5.2 does not currently support macOS 10.14 Mojave.
Please read our forum post
for the latest updates.
[Solved] Getting Error "You cannot use "xx.screensaver" with this version of OS X..
it's just 2 images with random and loop settings.. Using OpenGL - built with iScreensaver 5.1.1 on an ElCap Mac and being installed on an El Cap Mac.. any help would be greatly appreciated.