In the meantime, I helped a customer some time ago to work on RPMsg demo for Colibri iMX8X on Torizon OS 7.3.0. There are some patches and changes you need to apply for that. It is described here: /dev/ttyRPMSG30 not created in Torizon OS 7 on Colibri iMX8QXP - #30 by rudhi.tx
If you could try the same thing out for hello-world demo and test it, that would be nice. The SDK I used was SDK_2_9_0_MIMX8QX5xxxFZ and toolchain 14.3.