Ok, I finally found a solution to the black screen boot problem. Someone here in the forum said, that all we have to do is to use a HDMI cable and connect it directly to the monitor instead of using a DP cable from EGPU to the monitor.
This is what you have to do:
- Connect Mac Mini with your monitor using HDMI cable
- Connect EGPU with Mac Mini via USB C
Boot. You will see the boot screen, everything is like it is supposed to be. And you will be able to use the EGPU.
Although it will say in your Apple >About this mac info panel, that the internal GPU is being used, you will still see the egpu icon on the menu bar. Which means, that every app you checked with "prefer egpu" in the info panel will still use the EGPU, apps, games, etc. The only issue is that the UI will not use the EGPU, but you can optimize that by checking "Prefer EGPU" for the finder.app, etc.
For me this solves everything: no need for a headless HDMI dummy, no need to switch on the EGPU after switching on the mac mini, no fiddeling around with cables when updating MacOS, etc. - you will see the boot screen and EGPU is being used (as long as you checked the "prefer egpu" checkbox on every app).
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Some apps like the latest version of Final Cut or Photoshop, etc. have a setting within the preferences where you need to select the egpu. Both apps benefit a lot from switching to egpu use.