GoBDokumente is a macOS application
Since Apple broke the Safari user agent string

CCBot/2.0 (https://commoncrawl.org/faq/)

under macOS Big Sur, the automatic detection of which version of GoBDokumente you need to download is temporarily suspended and you have to manually choose which version you want/need to download:

Download Version 1 for macOS 10.11 - 10.15
Download Version 1.8.2 for macOS 11+
Download Version 2 for macOS 11.0+ (incl. support for M1)