I am trying to connect my 2020 MacBook Pro (M1) to an external display via a thunderbolt 3 dock.
The dock is the Kensington SD5200T which supports M1 Macs with 1 external display.
The screen I am trying to connect to is the ASUS PG349Q via DisplayPort (1.2).
The MacBook is running the latest version of macOS (Big Sur 11.2.3).
When I connect the MacBook to the dock using the included Thunderbolt 3 cable the internal display flickers (resolution changes, windows flash on and off the display) until it eventually connects to the external display (this can take upwards of 1 minute).
I made a video demonstrating the problem, it can be found here.
I have tried the dock and MacBook with an LG 5k thunderbolt display which works fine and I'm using the DisplayPort cable from my PC so I know the cable isn't the issue.
Does anyone know how to fix this?
Update:
I downloaded SwitchresX but unfortunately, it did not resolve my issue.
Then I tried a DisplayPort to USB-C cable connected directly to the MacBook but this also didn't work (no video output).
However, I tried connecting the dock's DisplayPort to the monitor's HDMI (1.4) port using an adapter and it works! I only get 50Hz instead of the monitors 120hz but at this point, I'll take this as a win.
Thank you to everyone who commented, I really appreciate the help.
Best Answer
Numerous people report issues with ultra wide screens (width > 2*height) and M1 Macs. By my count, there have been three questions here in the past week. There are 12 pages in this macrumors thread.
I suggest a web search for "Mac m1 ultrawide" to get a feel for the number of problems.
Apple have acknowledged the issue, but are yet to provide a fix. For a report on this 9to5Mac.
To reduce the number of uncertainties, try and get the monitor to work without any dock. When that fails, contact Apple.
I am aware that this "answer" does nothing to resolve problems with utrawides, it is little more than a pointer to it being a widespread issue.