Okay, after fighting with this for the last few hours, I seem to have finally found a solution so I'm sharing it here in case anyone else is having the same issue, or just so I can find it if I forget about it in the future.
I updated the Nvidia game ready driver for my 4080 last night to the latest version and during the installation process the screen went black as it usually does, but this time it did not come back on. I force restarted the PC and could enter BIOS without issue but the moment Windows started booting up, the DisplayPort 1.2 signal died. After playing around with my old monitor I realized the HDMI 2.0 display was working fine as long as the DisplayPort monitor was unplugged. I got an old version of GRD and installed it instead, which got my DisplayPort working again.
However, the old driver had some issues with G-Sync so I updated again, to version 595.76, as this seems to be the most stable recent version, but the same thing happened and DisplayPort signal went out during the update and wouldn't come back. This time, however, I plugged the HDMI cable into my current monitor, and I got HDMI signal. I could see the update finished, but my start menu wouldn't open so I force restarted the PC.
After the reboot, I was still getting the HDMI signal and decided I'll just use that over DisplayPort, but unfortunately it turns out G-Sync doesn't work over HDMI for my monitor (Gigabyte M32QC). So, I plugged in DisplayPort cable at the same time as HDMI and realized that I can now switch between HDMI and DisplayPort input at the same time. Unplugging HDMI cable would also stop DisplayPort signal. While both HDMI and DisplayPort were plugged in, I started playing around in the Nvidia Control Panel and realized that my monitor is being detected separately as 2 monitors, one connected via HDMI and the other via DisplayPort, with HDMI connection being recognized as the primary and DisplayPort as the secondary monitor. I swapped this around by disabling the primary HDMI monitor connection which automatically switched DisplayPort connection to the primary one. Once this was done, I unplugged the HDMI cable and DisplayPort has been working without issue since. And, so far, everything seems to work properly again.
So, in summary, if you lose DisplayPort signal after updating your Nvidia drivers, do the following:
- Plug in a HDMI cable in addition to the DisplayPort cable and switch the input on your monitor to HDMI. If there's no signal, unplug the DisplayPort cable and you should get HDMI signal.
- Reboot PC once you're sure the update is done (force reboot is fine if Windows Start Menu won't open).
- Plug in both DisplayPort and HDMI cable at the same time. Switch between DisplayPort and HDMI input on your monitor to make sure you have connection on both. DisplayPort desktop should have no desktop icons on it as it'll be considered a secondary display, while the HDMI input will look like your standard desktop with all of your icons.
- Open Nvidia Control Panel and go to 'Set up multiple displays' section.
- Disable the primary monitor connection (marked with *) by unchecking the box next to it and click Apply.
- Unplug HDMI cable.
This should revert the DisplayPort back to being your primary connection and giving you back the signal which the update removed. I have no clue why this works, but my best guess is that something is wrong with the new Nvidia drivers and they default to HDMI being the primary connection even when a monitor is connected with only the DisplayPort connection, but plugging in both HDMI and DisplayPort at the same time and then disabling HDMI allows you to swap DisplayPort back to being the primary connection. It's possible this would also work with having a HDMI and DisplayPort monitors plugged in at the same time rather than having both connections to the same monitor at once, but I haven't tested it.
This also means that having a HDMI cable is a necessity. Had I not had it, I would've had to format my PC as there was no way for me to get monitor signal via DisplayPort past BIOS, so I would have no way of reverting back to the old driver.
Surprisingly, this seems to permanently fix the issue, as I was able to use the Nvidia App to update to the latest 596.36 driver without losing DisplayPort signal again.
I hope this helps someone, or that Nvidia fixes this issue with their future drivers.