OpenGL is the only truly cross-platform graphics API out there. Vulkan isn't on Apple platforms, unless you use MoltenVK which implements it on top of Metal. Also I don't know why, but Windows games tend to use Direct3D even though afaik GPU drivers do implement Vulkan on Windows, so there must be a good reason for that.
It's also much easier to grasp than Vulkan, Metal, or Direct3D.
Contrary to urban myths, OpenGL never was a big thing on game consoles.
Windows official API is DirectX, OpenGL and Vulkan use a plugin API, ICD, which is nonetheless DirectX underneath.
https://learn.microsoft.com/en-us/windows-hardware/drivers/d...
OpenGL is deprecated and version locked on Mac/iOS.