Just want to let you guys know that I've fixed this! This was my reply on page 2: Same here. Macbook Pro 2017 13'' no-touch-bar model. Before updating to Big Sur, I connected to 2 external HDMI monitors with no problem at all. Just after updated to Big Sur, now one of the external monitor will intermittently flicker (flashing or black for 2-3 seconds then come back), especially after sleeping for a while.  This is really annoying and deminishing the usability of Macbook! Please fix this ASAP, Apple! And please give it a thorough test before releasing a new OS! - Then I re-installed Catalina. - The problem was still there! BUT it was much better than on Big Sur! Less frequency and less black screen time! Then I replaced my ThunderBolt adapter HyperDrive NET 6-in-2 Hub to the apple.com suggested CalDigit Thunderbolt 3 Mini Dock -Portable. The problem is gone! Then I upgraded to Big Sure again. The problem is gone! So my conclusion is it might not be Big Sur's problem, but Big Sur might maginfied the problem.

Same here. Macbook Pro 2017 13'' no-touch-bar model. Before updating to Big Sur, I connected to 2 external HDMI monitors with no problem at all. Just after updated to Big Sur, now one of the external monitor will intermittently flicker (flashing or black for 2-3 seconds then come back), especially after sleeping for a while. This is really annoying and deminishing the usability of Macbook! Please fix this ASAP, Apple! And please give it a thorough test before releasing a new OS!