it might be coming later because epic has on their future roadmap that they are implementing the metal-cpp sdk which includes the metalfx library.
I think that github is of a community fork but apple has the same thing on their website, apparently unreal still uses some super old metal API which was discountinued in 2018 and lacks support for things like metalfx, so hopefully with the metal-cpp api rework it will support options for it. it would be a huge boon for mobile developers on unreal engine.