Thank you for contacting us, I am sorry this is not working as expected.
I was able to reproduce this behavior with the UD-4VPD docking station with a 4K 120Hz television being limited to 60Hz. This also affects USB Type-C DisplayPort Alternate Mode 1.4 to HDMI 2.1 adapters and appears to be a limitation within macOS when connecting a high-refresh rate HDMI display to the computer via USB Type-C. As you noted, connecting with a USB Type-C to DisplayPort input on the display should not encounter this limitation.
I tested systems from a 2019 MacBook Pro with Intel processor, M1, and M2 MacBook Pro 13-inch and Air systems, 15-inch MacBook Air M2 and 16-inch MacBook Pro M2 with native HDMI output, all showed this behavior when connecting to a USB Type-C to HDMI adapter or docking station. The 16-inch MacBook Pro with M2 was able to support 4K 120Hz with the built-in HDMI output port.
To ensure the test setup had compatible cables and there were no hardware limitations I tested all adapters and the docking station using a Surface Laptop 5 which enabled 4K 120Hz for all adapters and UD-4VPD docking station tested.
I am sorry, this is a limitation in Apple systems independent of the Apple specifications and we will be updating our compatibility statements to reflect this behavior.
I can help to return this docking station for a full refund.
Please send an email to support@plugable.com with the subject line “Ticket #412238 - Attention Pat” and we can start the refund process.
Thank you, and I apologize for this inconvenience.
We’re closing this thread due to inactivity, but if you have any further questions please feel free to contact support@plugable.com and we’ll be happy to help.