Hi Matt,
thank you very much for your information.
From your answer I conclude that (except setting up Preshow via settings) I don't need to enable anything else (e.g. in Kodi settings or skin settings) or pay attention (so installing addon and setting it up is enough)?
Yes, then I'll wait for DexDeadly, maybe he has another idea what it could be.
Thanks again and have a nice weekend.
UPDATE:
Everything works as it should, even with Jellyfin.
It turns out that I was just a bit stupid, while looking around.
I thought the sequence would start automatically when a movie is played,
but had overlooked the option for Preshow Experience in the context menu.
Thanks again and of course thank you for the addon!