Believe you mean RX 580 and not an RX 850... correct?
As stated above, the RX 580 was officially made available by Apple under the eGPU Developer Kit and support for that card will continue for some time. It is NOT being sold by Apple currently.
Yes of course I’ve meant the RX 580.
I'm using a Sapphire RX 580 Pulse 8GB card in MyHero II hackintosh w/o any problems.
So you wouldn’t care about any „maybe problems“ reagarding Mojave right now?