I agree that OpenGL cannot be considered an “old” or dead API, but nowadays, there is a better alternative on almost every platform. Even the Raspberry Pi will add Vulkan support in their drivers in the near future, even though their OpenGL support is lacking yet (only their OpenGLES support is decent).
=>On Windows, there is DX12, a much more explicit and debuggable API (I’d argue Our Machinery should consider supporting DX11 as well, but it depends when they expect to release a stable version). It being the “official” API also helps (OpenGL support was a mess on Windows for a while).
=>On MacOS/iOS, OpenGL is deprecated, the better option is to add Metal support right now (and since Apple forces its users to update their OS as much as they can, Metal support is pretty widespread in the Apple ecosystem). I’ve also heard that Metal is nice to work with, but I haven’t practiced it myself.
=>There is now quite decent support of Vulkan for Linux, and on Android, Vulkan has been there for a while now
=>On consoles, it’s always a better option to use the dedicated API. (I worked it a team that ported a game to the PS3 while trying to keep their OpenGL backend, and it did not go well). Modern consoles’ APIs are getting nicer and nicer, and their community of developers is more willing to help you when you use them than when you try to keep a multi-platform API. The Switch’s one is a pleasure to work with.