I tried the Raspberry Pi 7” Touch Display and DIsplay 2 using the Raspberry pi 5 cable and nothing appeared on its own or with an HDMI attached as well.
I tested the same cable and power on a Raspberry Pi 5 and both displays work. It was my understanding that the ILI9881D driver IC (which works out of the box) was used on at least the Touch Display version 1. Is that incorrect?