this may not be the case, but from what you told me, it has various similarities, so don't discard this possibility
maybe is your monitor that started to give in? if the screen flashes green for less than a second and go back to normal instantly, that may be a sign that your monitor was damage to some extent
you can run a simple test to determine this: lower your resolution from 1080P to 720P or lower, if the flickering stops (or significantly reduce) that may be a dead giveaway that monitor is straining itself
but the proof is in the pudding, if you still not sure that's the case even after that test, trying using a different monitor, any standard TV set nowadays have an HDMI input, you can try to use another household's TV to test that, if there is no signs of flickering or random flashbangs, you may need to replay that monitor very soon, as it's warning you that your monitor is on it's last legs