While USB C DP/HDMI Alt Mode doesn't require USB 3.x, it is quite commonly known that most manufacturers won't implement the mode with USB 2.0. Instead, they opt for 3.x to have the feature for whatever reason. Any subsequent Xiaomi devices come with USB 3.x support which gives them this mode. Heck, even Xiaomi 13 Ultra which is the closest one to Xiaomi 13 Pro also has the feature. Xiaomi 13 Pro is just a little too early when released.