I happened upon these interviews on a podcast by two German former game journalists (not paywalled; the interviews are in English, after a short introduction in German):
And for people who understand German, here’s an interview with Guido Henkel in German from 2019: Stay Forever Podcast
(this was actually what led me to find the podcast, as I was looking for information on his game “Drachen von Laas”, prompted by rovarsson’s question in another thread)