Hello everyone,
I developed this website (GoDaddy WordPress managed hosting): http://el-cuervo.de/
The website is accessible from every corner of the world, except in Germany. My client from Germany can't access it because of this error. The website itself is hosted on GoDaddy. We tried everything, new device, new network, cache flush, no plugins, and nothing worked… GoDaddy support is also useless since they just say "We can see the website with no problem, it's not us." which is insane, 0 effort to solve this issue. What should I do? Switch to another hosting or keep attacking GoDaddy.

Idk godaddy. But possible that you blocked Germany? Or that the specific server is blocked in Germany?
You answered your own question anyway, regardless what the bigger issue is – Switch to another hosting.
I get a certificate error and an internal server error from the USA.