I'm stumped about how to get the alpha blended transitions in slideshow - everything I have tried hasn't worked.

I've looked at several threads including this one:
https://irfanview-forum.de/showthread.php?t=510
So I've gone to Properties/Settings, selected Full screen/slideshow, selected the alpha blended transition. In I've also selected full screen mode in Slideshow settings box. I've tried different jpg and gif files, different ways of opening them but still can't get anything other than a sudden transition.

Can anyone help me please?

Thanks!