依據 USB4 spec 1.0 ， USB3 adapter layer 對於 gen2 dual-lane (2x2) 只是 optional ，大部分的情況下沒支援也不意外...

9.2.1 Link Layer
An internal USB3 device port that interfaces to a USB3 Adapter Layer shall implement a Link Layer as defined in the USB 3.2 Specification with the modifications, configurations, and parameters described in this section.

The Link Layer shall support Gen 2 Single-Lane (2x1) and may support Gen 2 Dual-Lane (2x2). No other Link capabilities shall be supported.

An Internal USB3 device shall not send a LBPM PHY Capability with a value of 0 in bits [3:2].

Note: The USB3 LBPM handshake between the two internal USB3 devices ports determines the link that will be established.

至於 USB4 支援 TB3 20Gb/40Gb 的部分，那就跟 USB 關係比較小了

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剛看了一下，這板子還有一個寫 SS20 的 2x2 port ，支援 20Gb/s 應該是這個吧？