With a nVidia GTX 760 the monitor was turning on at boot, in time for me to see the Award logo and to enter the UEFI BIOS. The BIOS is set to "other OS" (vs Windows 8) and secure boot is disabled because I also have macOS installed on the same computer.
Since I installed a Gainward GTX 1060 6GB Phoenix in the same slot previously used by the GTX 760, the monitor turns on but it's empty and I get the message of no signal available, until the login screen of Windows 10 appears. No booting screen is shown.
I tried both "normal BIOS" and "backup BIOS" (the physical switch) of the GTX 1060.
I tried to enter the UEFI and I think it works, because after an unusual time I was still waiting without W10 login screen, but I couldn't see anything.
I'm especially worried because probably I won't be able to see the "Windows updating" boot screen and that means that sometimes I will have to wait without any idea why and because I won't be able to access the UEFI in case of need. Also, no access to macOS.
Drivers and UEFI are updated. I have no way to know if the GTX 1060 BIOS is updated, since there are no updated available by Gainward.
I tried all the three Displayport connections.
How can I solve the problem and see the bootup process normally?
Following the suggestion from the comments, I tried again all the ports. With Displayport 1 I get the behaviour described.
With Displayport 2 or 3 the boot does not proceed, I guess, because everything is black and brief-pressing the power down button brings down the PC immediately, while it should take some seconds if the login screen were ready (albeit invisible).
With HDMI I can see again the boot process. This means that somehow HDMI is the first display.
The question stays: how can I see the boot again, with Displayport?