Since writing the above post, the Avent Display and Cameras arrived.
Seems camera is nice and easy, plugged it in and works with the camera App straight out of the box.
Plugged in the Display and does not light up or do anything.
Looking at the spec sheet it seems it pulls the power from the Mipi Disp socket and does not need separate 5V supply. Also back light pulls power from connector also, but nothing lights up on it.
Are you using the correct DTB? Please refer to MaaXBoard-Linux-Debian-UserManual-V1.2-EN page 11. You need to modify the uEnV.txt file in the OOB image to set the fdt_File = em-sbc-imx8m-dcss-dsi.dtb
