Since DXVK (Running DirectX 11 native over Vulkan in Wine on Linux) runs DX11 a bit different than native Windows, i'd like to know if this is considered "modifying" the Game in such a way, that it does contradict the licence agreement.
Basically, will i get banned for doing such a thing? (Maybe i should post that in the support forum?)
While the Support folk would be your best bet to get an answer about what Frontier thinks on this, I will say that Frontier does not own DirectX 11 or Vulkan.
DirectX 11 is the property of Microsoft, and even suggesting that it might be otherwise is a violation of at least 9 different Microsoft End User License Agreements and can result in the most severe of penalties, up to, and including, being forced to become an iOS Darwin user for three reincarnations.
Vulkcan is a sort of kludge of things AMD couldn't figure out how to make work (Mantle) and bits of OpenGL. Like most things Linux-based, no one really cares what anyone does with it.
And I'm not even an anti-Linux person - I actually like it, I just don't want to put that much effort into trying to have fun and hoping that it works at least 80% as well as in the environment where it was intended to run.
That said though, I do run a Linux-based mail server, PXE server, router for my render farm, and a Linux VM for when I want to fiddle around in Linux.
Sadly, Linux will never be a substitute for actual Windows for running Windows-based applications - it just won't. I accepted this as immutable fact well over two decades ago. The whole "trying to get X to run in Y" is just not time well spent and not worth the effort.