Apple iPad 6th gen (apple-ipad7,5)

A mainline fork for this device is available here with further instructions here. Still needs to be tested and ported to postmarketOS.

How to enter flash mode
Plug in the cable, hold Power and Home key for 2-4 seconds for device to power off completely, so the backlight is dimmed, then release the Power key and continue holding the Home key for 8 seconds until you get a new DFU device.