External display wakeup problem
 

In a Three-Monitor setup (iMac built in Monitor, one DisplayLink monitor and one monitor connected directly via USB-C), the third monitor directly connected via USB-C does not wake up from sleep as long as the DisplayLink Screen Manager app is running.

I have a LG Ultrafine connected via USB-C to my M1 iMac. As long as Screen Manager (including 1.6 beta) is active, the LG Ultrafine does not wake up from sleep.
I need to disconnect/reconnect the monitor in order to get it back to work.

I also have this problem and a similar 3 screen setup - what Dock are you using? If it is a Dell D6000 have you previously updated the firmware? The issue had gone away for me before installing the 1.6 beta to enable screen rotation.