
I believe this feature is GPU-independent because the two AMD cards tested all worked ( RX 480, RX Vega 56). Which macOS version are you running on your 2018 Mac mini? I will check later today and post Boot ROM version if it's different than 1037.0.39.151.1 (iBridge: 1.5.4,0) from 10.15. I have not tried rEFInd recently but don't see why it wouldn't work. I can access the Startup Manager natively as well as automate-eGPU EFI. I tested mine and it worked by holding OPTION at boot. Following Dev Beta 5 on July 31st is when noticed this new Boot Screen support on his 2018 Mac mini with monitor through eGPU only.
