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] "Flash Plugin not installed" in small preview on Windows 10
My Flash-based screensavers created with iScreensaver Designer 5 work just fine on Windows 10, but in the Screen Saver Settings panel there's always an error message stating "Flash Plugin not installed, unable to display X.swf. Please install the Flash Player Plugin". See: http://i.imgur.com/7LQFRpq.png
Can anything be done about this?