Germany did not invent döner kebap and it's insane that they claim that. Anyone who insists on it displays a tragic lack of understanding about what a kebab even is and should be ashamed of themselves.

What they did invent is their own way of preparing and serving döner kebab, an existing dish that is itself a variation of other existing dishes that came before it. In the kebab world, that's not only allowed but also basically encouraged. Everyone is welcome to modify dishes to their heart's desire. There are countless kebab dishes in Turkish cuisine that are nothing more than slight variations on existing dishes. What you should do after creating your own variant, however, is to also give it your own name to mark the difference. That's what the Germans have not done. They're continuing to use the name of a dish they did not invent. That's a bit of a dick move. Seriously, look up Adana kebab and Urfa kebab. They're essentially the exact same thing except one is hot and the other is not. Yet they have different names, because that's how it's done.

The German döner kebab is a distinctly different thing than the "real" döner kebab. According to the long standing kebab traditions, it must be given its own name. Otherwise no, döner kebab was most certainly not invented in Germany. Name it something else and make a proper claim. It would even help enrich your exceptionally poor and boring cuisine a little bit.