Screen randomly flashes black for a second while gaming

if you're on gsync or freesync, turn it off as a test. some monitors blank out for a second when the frame rate drops below their VRR range. and if you pushed the refresh rate past stock in the monitor's settings, put it back.

Swap the cable first. A loose or cheap HDMI/DisplayPort cable is the usual cause of a one-second blackout, especially at high refresh rates. If that doesn't fix it, update the GPU driver with a clean install, since a driver that crashes and recovers looks exactly like this.