Only AMD graphic cards work fine natively since HS. The problem was that people wanted Nvidia support, they had web drivers from Nvidia for HS but there is no Mojave version yet IIRC.

Apple has only been supporting AMD graphic cards natively with macOS since the beginning and they never said Nvidia GPU would be supported out of the box nor do any of their docs say it is. They have a strict list of supported eGPU boxes and GPU for each boxes (https://support.apple.com/en-us/HT208544).

eGPU support in macOS has been crappy at the start even for AMD cards but they've been steadily improving since then. The problem is Apple takes forever to improve their support after only offering the option to use eGPU for certain apps in Mojave.

Nvidia drivers are likely (I doubt given Apple's recent history track) to be added to macOS when they release the redesigned Mac Pro later next year as they'll need to support various cards. Right now, there is no Apple device with Nvidia cards, so no drivers either.

On the other hand, Apple may just do the silly thing of releasing Mac Pro with no chance of changing GPUs. If this happens, there will not be any chance of Nvidia drivers for a long time.

Apple hasn't quite tightened the noose of lock-in on OSX as much as they have on iOS.