Thanks for sending the diagnostics. Looking at them, I see your MacBook Pro 16" currently is detecting the dock as I would expect, and I can verify I also see the 30Hz issue. I also see your Mac appears to be on the latest macOS Big Sur 11.2.3 version.
Here’s what the system is reporting for your display, the resolution and refresh rate both look incorrect (reporting a “6K” display at 30Hz):
LG Ultra HD:
Resolution: 6016 x 3384
UI Looks like: 3008 x 1692 @ 30.00Hz
Framebuffer Depth: 30-Bit Color (ARGB2101010)
Main Display: Yes
Automatically Adjust Brightness: Yes
Connection Type: Thunderbolt/DisplayPort
This behavior may be related to some problems we’ve been seeing since macOS 11.1, where something changed in the OS that has caused incorrect resolutions and/or refresh rates for displays attached to Macs directly or through a dock like ours. You can see here it’s been a rather large issue affecting many users: https://www.macrumors.com/2021/02/03/macos-big-sur-external-display-issues/ We may be unable to resolve this behavior until a new version of Big Sur is released which addresses these problems users are experiencing. Unfortunately it appears the latest 11.3 beta is still affected.
For what we can do to try and resolve the issue, or at least improve behavior for now, I’ll make some recommendations below:
- Unplug the dock from the Mac
- Perform an SMC reset: https://support.apple.com/en-us/HT201295
- Perform an NVRAM/PRAM reset: https://support.apple.com/en-us/HT204063
- Plug the dock back in to the Mac and see if the behavior has improved
If that hasn’t helped, we can try to manually override the settings macOS is offering you:
- Choose Apple menu > System Preferences, then click Displays.
- Choose the display that you’d like to change the resolution for, then hold the Option key and select the Scaled button . Then the refresh rate drop down menu should appear.
Example (with the built in display):
To try address the other issue with this display not being able to stay in sleep mode correctly, I have heard of this behavior in a few other customer reports with this dock, but never before with this model display. This is the first report we’ve received with this monitor model being used with this dock.
Researching this monitor for possible clues to the sleep behavior I did not find anything that matched your description of the sleep problem, but others on Mac are seeing some other troubles too: https://discussions.apple.com/thread/8526209