Like a number of folks, I recently switched from a Mac Pro 2010 to a Mac Mini 2018 and overall I've be quite happy with the change. I purchased a Razer Core X along with the Mini and installed the Sapphire Pulse RX 580 that I had been using with the Mac Pro (running Mojave).
I have two ancient displays, Apple Cinema Display and Apple Cinema Display HD (both on the "to be replaced as budget allows" list). And like a number of folks, when I start up the Mini I get black displays. My solution had been to attach one of the displays directly to the Mini, via HDMI. This worked, in that both displays were now recognized at startup. But the one connected to the Mini had a pink line down the left edge. Annoying, but usable and as Fishrrman has noted on this forum, find something that works and stick with it (although I would add, keep looking for better solution).
I also have an old iPad, an original iPad Air. And I had recalled that an iPad could be used as the only display for a Mini. The Mini came with Catalina installed, and Catalina has Sidecar, but my iPad is too old. Very sad. But not too old for Luna Display.
And my Luna Display arrived today. I followed the instructions the the Luna Display folks provide for using the iPad as the only display for the Mini, found here: https://lunadisplay.com/pages/using-luna-with-mac-mini, hooked my two displays to the eGPU, and I can now startup using the eGPU with one caveat, the eGPU has to be turned off until the iPad connects as a display for the Mini. After that I switch on the eGPU and I'm good to go.
This won't work for everyone as the Mac needs to startup without entering a password, but I'm ok with that. It's not optimal and I'll keep hoping for a true solution from Apple. Until then, it works for me.
I have two ancient displays, Apple Cinema Display and Apple Cinema Display HD (both on the "to be replaced as budget allows" list). And like a number of folks, when I start up the Mini I get black displays. My solution had been to attach one of the displays directly to the Mini, via HDMI. This worked, in that both displays were now recognized at startup. But the one connected to the Mini had a pink line down the left edge. Annoying, but usable and as Fishrrman has noted on this forum, find something that works and stick with it (although I would add, keep looking for better solution).
I also have an old iPad, an original iPad Air. And I had recalled that an iPad could be used as the only display for a Mini. The Mini came with Catalina installed, and Catalina has Sidecar, but my iPad is too old. Very sad. But not too old for Luna Display.
And my Luna Display arrived today. I followed the instructions the the Luna Display folks provide for using the iPad as the only display for the Mini, found here: https://lunadisplay.com/pages/using-luna-with-mac-mini, hooked my two displays to the eGPU, and I can now startup using the eGPU with one caveat, the eGPU has to be turned off until the iPad connects as a display for the Mini. After that I switch on the eGPU and I'm good to go.
This won't work for everyone as the Mac needs to startup without entering a password, but I'm ok with that. It's not optimal and I'll keep hoping for a true solution from Apple. Until then, it works for me.