Sorry that the slideshow is coming out blank when you preview or play it in Lightroom Classic CC. Which version of Lightroom Classic CC are you using?
Could you please uncheck "use graphics processor" under the Preferences> Performance menu in Lightroom and let us know if you're able to preview/play the slideshow?
No idea why, but obviously you have an idea
Forgot the version information
It is LR Classic CC version 7.4
you probably have seen the reply. Thanks
version is LR classic CC 7.4
this might help you. The graphics card is Intel Iris Graphics 6100