It was a surprise for many gamers to find out that that Cyberpunk 2077 does not work on Windows 8 and Windows 8.1 as of the release date (December 10, 2020). Attempts to launch the game result in the immediate crash and "flatlined" error message.
Official explanation is that the game requires DirectX 12 API, and Windows 8 doesn't support it, while both Windows 7 and Windows 10 do support it.
Word on the street is, the game doesn't actually need DirectX 12 at all, since it works on platforms without it, such as Playstation 4 and Stadia.
Supposedly game already supports Vulkan API, and uses it on Stadia platform instead of DirectX. And the latest delay of the release of the game was possibly there to implement Vulkan and Stadia support.
So why not release Vulkan version to general public? Since game developers were already overworked hard to get the game to release on date, they might have had not enough time to test Vulkan version properly, or they might have had an agreement with Microsoft preventing them from releasing the game with any other API.
Still, there is a hope that Vulkan version of the game will be released in the future.