I noted this in https://news.ycombinator.com/item?id=48079649

I also pointed out in that comment that USB-C debug accessory detection does not support orientation detection - and neither does the Google adapter you linked (it doesn't use debug accessory mode, and doesn't have some other solution either). As they say: "Determine correct orientation - top vs. bottom - the tool operates correctly only when SBU1 pin corresponds to TX and SBU2 pin corresponds to RX."

The fact that you can't detect orientation in debug accessory mode is a direct result of how it works: both CC lines are connected to the peer; normally the cable pulls one of the two to ground which is then your orientation reference for all the other pins. (This is also why you can't use a regular USB-C receptacle for debug accessories, it has to be direct to plug, the 2nd CC line doesn't go through the cable.)

So, if you use the SBU pins, it's not reversible anymore. If I remember correctly, debug accessories must still put USB on D+/D-, so the remaining option is to put serial RX/TX on the high speed pins, twice each on 180° positions.