As a hobby I play with Godot, a reasonably mature open-source cross-platform game engine. The current series, 3.x, uses OpenGL as the foundation of their Mac support. But they're also taking seriously the Apple deprecation of OpenGL, and the 4.x series under development (and likely at least a year away) will use Vulkan where supported, and MoltenVK on the Mac and iOS.
It would make a great great deal of sense for Apple gaming if Apple decided to officially support Vulkan, or even to officially support MoltenVK. But they don't.
As pointed out some three years ago there is (or as least was) a good reason for that:
"Both are still young although
Metal was released in 2014 and Vulkan was officially released in 2016, so they do overlap in certain features,
the benefits for Metal 2 was performance and API make it easier for partners and developers to write than in Vulkan, Vulkan developers share their experiences that Vulkan is hard and yes, fragmentation probably make it more complicated since some features is not available for older devices" -
Vulkan vs Metal 2 (Reedit)
Basically not only was Vulkan two years late to the party but only year after it came out Apple was to Metal 2. Then Apple came out with Metal 3 June 2019. And where is Vulkan now? Puttering around at Version 1.2 and, odds are, still royal PITA to use.
A comment 4 years ago on Apple's developer forums,
Vulkan and Metal (some observations), said this:
"Metal still does a lot of hand holding and behind-the-scenes management for you, while with Vulkan you are responsible for — literally — everything. And man they were NOT kidding when they said that the API is explicit. Its actually quite ridiculous how
diffficult and detailed the API is. (...)
The explicit nature of Vulkan might offer additional optimisation opportinuties to applications seeking to squeeze those 100% out of the hardware,
but at the extreme expense of usability.
Metal is a more casual API, which is very convenient to use and still offers very good performance (and performance guarantees) that will satisfy an overwhelming majority of applications, both for graphics and compute. With some extensions, it will basically have feature parity with Vulkan, and it can easily borrow some of Vulkan's optimisations without sacrifising ease of use (e.g. batched binding updates, reusable command buffers as well as synchronisation primitives). And let's be honest here — applications that really need explicit control like Vulkan provides are high-end game titles, which are not targeted at the Apple platform anyway (because they require really beefy GPUs, which Apple simply does not ship in their machines).(...)
I think Apple might have lost the initial interest in Vulkan after they saw what it was shaping up to become. They were interested in having a convenient and efficient replacement for the difficult to maintain and erratic OpenGL.
Vulkan is certainly efficient but I wouldn't call it 'convenient'. Its not an API that would draw developers (especially small-time developers) away from using OpenGL or encourage them to make more titles for OS X. "
Elsewhere there was this: " Plus people need to remember DX12 and Vulkan offer CPU performance boost,
major GPU boost is not on the table." Metal, by contrast is aimed at the
GPU. This is the other reason Apple went with Metal rather then Vulkan: why would you use a graphical API you have to fight with to use the GPU because it wants to be Captain Clueless and use the CPU by default?!
As for MoltenVK: "MoltenVK has picked up support for a number of new Vulkan extensions and other fixes, but now does
require Apple Metal 3.0 A Metal 3.0 requirement means using Xcode 11 for building and targeting macOS 10.15+ and iOS 13+ for the run-time requirement. MoltenVK still supports their earlier v1.0.36 release without Metal 3.0 for those wanting the older iOS/macOS coverage" (
MoltenVK Now Supports More Vulkan Extensions, Begins Targeting Metal 3.0)