I have a new MacBook Pro (13-inch, M1, 2020) running BigSur 11.4 (20F71) and I have an LG 4K flat panel connected to the laptop via DisplayPort using a Thunderbolt to DisplayPort adapter. When I put my MBP to sleep (not power down), the 4K monitor keeps powering on and off again. When the MBP is actively running, there are no issues with the display. This happens with both an LG 32UD60-B and LG 32UD59-B. I have disabled all notifications that can popup when the MBP is sleeping, disabled Wake for network access and removed legacy (x86) apps that like to periodically wake up and check the status of things. The MBP’s screen will not turn on however (not unless I wake up the MBP).
I have been reading about this issue with Big Sur and DisplayPort connected external monitors. I have tired several different Thunderbolt to DisplayPort adapters and a hub with a built-in DisplayPort interface (the CalDigit TS3 Plus) but the behavior remains the same.
The monitor does come up properly when I wake up the system, so I’m not experiencing the “black screen” issue that other users using DisplayPort connected monitors have reported.
I am using a Plugable USB-C Dual 4K DisplayPort Adapter with Gigabit Ethernet for Windows connected to the Thunderbolt 3 port on the CalDigit dock. Because I am using an M1 system, I have to run DisplayLink to be able to use the LG monitor connected via DisplayPort to the Pluggable adapter. Interestingly, only the LG monitor that is connected to the CalDigit DisplayPort connector (or directly to the MBP via a cheap TB# to DP adapter) exhibits the “wake up periodically when the MBP is sleeping” behavior, the other LG monitor that is connected to the Pluggable adapter and which is driven by DisplayLink does not wake up when the MBP is sleeping (and it does wake up properly when the MBP wakes up). So I think based on a lot of reading online, Big Sur has a bug in it’s DisplayPort driver. I have posted this to DisplayPort connected monitor periodically wakes up when system is sleeping (Apple Discussions) in the hope that someone there knows more about this issue.