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I have a Surface Thunderbolt 4 Dock with a Surface Book 3 running Windows 11 25H2. Windows Update and Surface app say my Surface and Surface Dock are up to date.
I'm trying to connect two external, older BenQ monitors. The monitors are 1920x1080 and only have DVI and VGA ports, so you can clearly see they're older and I'm not trying to connect crazy 8k monitors or anything. I've also turned off the internal Surface display via the Settings app as I only want to use the external monitors when plugged into the Dock. The monitors are connected to a dock via a USB-C to DVI adapter, both plugged into the rear USB-C ports of the dock.
Only one external monitor will be detected at a time. The USB-C to DVI cables work fine as each monitor will turn on if I unplug the other. But why won't both external monitors turn on?
Answer recommended by moderator
Found the answer on Reddit that is clearer than Microsoft's documentation.
No matter what resolution your monitors are, if the computer is not Thunderbolt 4-compatible, the Surface Thunderbolt 4 Dock will only use one external monitor no matter the resolution of the monitors. There is no full support for video out over plain USB-C.
