Second monitor keeps on temporarily going black at random

Fair enough.

I'd come to the same conclusion in your case.

For me, I either get the issue or not when I turn the second monitor on. Or it'll be triggered by launching certain applications that trigger G-sync. But nothing I do power wise ever triggers it when it's working correctly.

The GPU can be running at max and I might have zero problems or i can be idling with low power consumption and the screen flickers constantly.

I'll know immediately if I'm gonna have issues when I turn the second screen on.

I'm wondering whether there is more than one issue being discussed here. For the last few years I ONLY experienced the problem when I turned my desk fan on or off - the 2nd monitor would go blank for 3-5 seconds (not a "flicker", per se, but several seconds of darkness before turning on again).

Since upgrading to Windows 11, and replacing both monitors and both cables, the problem happens less frequently, but almost always occurs when I plug a small device into a gang socket on my desk. It has occasionally happened while doing nothing in particular - e.g. just two web browsers open, no video or gaming. But that hasn't happened for a few weeks.

So I'm pretty convinced that, in my case at least, power fluctuations are playing some part in this.

Lowering the refresh rates never resolved it for me - mine are both set to the minimum (60Hz).

There are also alot of Linux users reporting similar symptoms, going back years. Here's an example of one: https://www.reddit.com/r/Ubuntu/comments/18w4253/ubuntu_screen_keeps_turning_off_for_a_second_and/ I've had this with both Windows 10 and Windows 11. My money's still on the display adapter and/or HDCP, probably related to power supply issues (it used to happen every time I turned my desk fan on or off).

I refuse to believe that this is a hardware problem. We know for a fact that lowering refresh rates reduces or eliminates the problem entirely, but this is an unacceptable fix. We are not able to fully utilize our hardware as intended. Any power supply swapping etc could simply be placebo. I believe the problem lies within Windows itself, and the power management there. Many users indicate fixes revolving around this system, but it does not fix for all, as not all have the same system specs and use-case scenarios.

I, for one, have a three screen set-up for gaming.
3090 ZOTAC

i9-10900k

800w power supply

one monitor at 1080p 120 hz
another monitor at 4k 120hz
85" sony 4k at 120hz.

After trying a user's suggestion of turning off gpu hardware assist in settings-display-graphics settings the issue actually got worse.

I dealt with this problem over and over and it's my sony tv that is going black, which I use for computer gaming on couch with controller. Eventually I caved and set everything to 60hz and never had an issue. Only to reset back to 120hz a year later to see if a gpu driver or windows update fixed the issue, and it hasn't.

Any luck finding a fix? Clearly this is a widespread issue.

Also, I am experiencing the blackouts with my only HDMI connected output source (sony tv)

I have tried every possible settings combination for both windows and the tv display settings as well. Only lowering to 60hz eliminates the issue entirely. I believe you could be on the right track with hdcp handshake and power fluctuations. I have yet to try and use displayport for the tv, as that would be alot of work to run a new cable through a wall into another room.

I'm considering getting a HDCP defeat device or software to try and solve this issue.