Hello Gavin Lee,
Welcome to Microsoft Community.
I have noticed that you have tested this screen and USB-C cable on other laptop devices, so I am fully confident that this monitor and the USB-C cable you are using are fine.
After investigating the display, I noticed that it has two USB-C ports, but only one of them supports video transmission and the other only supports power:
HUAWEI MateView GT 34-inch Sound Edition Specifications – HUAWEI Global ****
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So just to be on the safe side, I recommend you double check if it's possible that you're connected to the wrong USB-C port.
If you make sure the connection is correct, after fully reading the question you posted here, please allow me to attach my judgment here. I think this is a third-party device compatibility glitch with the Surace Pro 9.
The best way to do this is to configure a dedicated Surface Dock for your Surface:
Buy Microsoft Surface Dock 2 – Microsoft Surface
Buy Surface Thunderbolt™ 4 Dock (Ports, Compatibility, Price) - Microsoft Store ****
They are all designed for Surface with unparalleled compatibility.
Alternatively, you can contact Huawei customer support for further debugging:
Best Regards,
Mitchell | Microsoft Community Support Specialist