“Uberspace doesn’t even host youtube-dl – it simply hosts the youtube-dl homepage, which links to GitHub.”
The RIAA’s DMCA takedown against youtube-dl failed in 2020 and GitHub put the repo back. So Sony, Warner and Universal went shopping for a friendlier court in Germany. Their target is a small host that serves a homepage with a link on it. Forum shopping against the smallest player you can find is not a legal theory. It is intimidation.