I just upgraded to Big Sur 11.4 from Catalina 10.15 on my MacBook Pro (16-inch, 2019). It completed without error.
Everything is fine, except...
Randomly, approx once per hour, but can be as little as a couple of minutes apart, the entire screen goes black for about 1/2 second, then it returns to normal.
This never happened before the upgrade.
Any ideas on how to stop this behaviour?