I have a Mac mini (late 2014) that I'm connecting to a 4K Iiyama B2875UHSU monitor. When I connect it via HDMI all is good. But I also want to connect my Switch to this monitor and since that only has HDMI output that is taking the single HDMI input on the monitor.
So I need to connect something to the monitor's full size DisplayPort port. I have tried various cables (HDMI -> DP, mini-DP -> DP) but when I connect those the Mac doesn't seem to boot properly. I can tell because the light on the wired mouse doesn't light up. When I boot the Mac without the cable connected (a mini-DP -> DP cable) it boots fine and when I connect the cable after it has booted I also get a picture without issues (proper 4K resolution). But when the cable is connected (tried with two separate miniDP->DP cables) the Mac simply won't boot.
In the past this same Mac mini was connected to low res monitor with a miniDP dongle that connected to a VGA cable. So booting with something connected to the miniDP output doesn't seem to be the issue perse.
I've reset the PRAM with no luck. I've tried multiple cables. Tried both minDP output ports.
Is there anything that might cause this behavior?
Update 1: When I boot the Mac mini with the monitor powered off it will boot properly. After switching the monitor on all worked fine. It seems something is happening in the communication between the two devices during (re)booting.
