DXVK was the last (IMO) major key in enabling proper Linux gaming.

Here's a short interview with the creator of DXVK.

Prior to this Wine was able to run some simple Windows applications, but games (which heavily rely on GPU acceleration) lagged quite a bit behind since DirectX is a Windows exclusive graphics API. Instead, on Linux we have Vulkan which is similarly feature rich, but an open standard. DXVK translates DirectX API calls to Vulkan, which GPUs on Linux can understand, similar to how Wine translates Windows syscalls to the Linux alternatives. Even though Wine existed for a long time, DXVK's development started quite a bit later.