https://bugs.winehq.org/show_bug.cgi?id=45626
--- Comment #4 from Rastafabi f.platte@platte-web.de --- To be sure I also ran:
defaults write org.winehq.wine-staging.wine GPUSelectionPolicy -string preferRemovable
though this did not change anything. I tested the detection with the Burnout Paradise Config Tool, as this allows selecting the GPU (on windows, and thus at least reads the currently used GPU. Whatever I do it still detects the Radeon RX 460 (my MacBooks internal Radeon Pro 560 - same device ID) but not my external RX Vega 56.
That said a fix is being implemented for a fork of the macOS Wineskin application by the developer of Porting Kit (Portingkit.org), which apparently already passes some additional GPU information to the running wine processes. I was told, that this functional is being expanded with eGPU support in a coming release.