Can not delete world

Cloned the world Arthandor and played a bit in there recently. Now I want to delete it but the delete button is greyed out.

0193e0e7-ca77-7b4c-9eb3-4637181596bc

I also have one question: Are we not allowed to change the theme of a world once we build them? It was possible before the last update but now it seems to not work anymore. Tried this with cloned worlds as well as with my own and not one I could change to another theme. Kinda sad, sometimes a more modern Urban Fantasy or Post-Apocalyptic Faladrim for example was refreshing to play after all the Fantasy sheningans.