Mac Mini 2018 + eGPU boot screen support in Catalina 10.15 Beta 5
Until Mojave the Mac Mini had no boot sector/boot screen support when the Display was attached to an eGPU.
I just installed Catalina beta 5 which updated the Mini's firmware during installation. Now my Mini 208 seems to have proper boot selector and boot screen support through eGPU (wich means a nice shiny high resolution Apple logo displayed on my 4K display during boot or the standard boot selector when pressing the Option key before boot). Not all roses yet, since usually instead of the login screen the OS boots to a blank white screen (I have to turn the eGPU on and off briefly to get the login screen), but the direction of the change is most welcome! I did not test this, but probably this change means proper FileVault login support as well!
I updated two of my headless Macs to Catalina Beta 5 last night. The 2013 Mac Pro was tested with newest builds of Purge-Wrangler. The 2018 Mac mini was not tested but I'm very excited to hear your update. Having the boot screen support through eGPU is a huge deal! Can you provide more information such as cable connection whether there's anything display connected to iGPU? Currently my boot screen is through USB-C port to an ASUS USB-C portable monitor. The eGPU connects to a different monitor through DisplayPort cable.
Hey, I tested the following scenario:
Both the HDMI and USB-C video output on the Mac Mini was fully disconnected, the sole connection was through the eGPU's DisplayPort output. The Apple logo appears within a second of system powering up and the Boot Selector is available and working if I hold the Option button pressed during power up (which indicates that the change regarding pre-boot eGPU support was made on a firmware level on the Mini).
My Mac Mini's Boot ROM version (I don't have a non-Catalina beta 5 machine to compare):
1037.0.39.151.1 (iBridge: 17.16.10521.5.4,0)
@steve4332 I can confirm macOS Catalina 10.15 Beta 5 [19A526h] brought eGPU boot screen support! This was tested on RX 480 and RX Vega 56. Boot Selector worked great for me with automate-eGPU EFI too.
As seen in the photo below, 2018 Mac mini connected to VisionTek mini eGFX + RX 480 which connected to HP Z27q via DisplayPort. I use @goalque's automate-eGPU EFI so that what visible on the external monitor. No display was directly connected to the Mac mini.