From the description supplied in support case the digital pins via the ribbon cable are not compatible with serial communication, as such are not wired to each other in anyway since the other side with 4 pins is a serial connection.
Sent from Mail for Windows 10
From: W9THC CriP Sparks
Sent: Friday, June 19, 2020 5:46 PM
Subject: Re: [BITX20] Nextion breakout ribbon cable for v6 #nextion #v6
Why not just use your ohm meter and prob the connector while touching the pin on other side Id imagine you would get continuity on the corresponding pins??