RDM IS WORKING?

You have also to tell the system on which XLR port RDM shall be used. Threfore go to the Output Configuration and change the Mode from Out to RDM on the desired RDM ports.

DMX Port Configuration - grandMA3 User Manual - Help pages of MA Lighting International GmbH

I'm asking this also because I've worked with RDM before but when I'm trying now no show any device.

Also make sure to add the RDM window to any of your views. I was expecting the RDM fixtures to magically show up in the Patch, which they don't. You need to add an RDM window, then they show up nicely.

In addition, there are two places where you have to activate RDM:

1.) Settings > Network. Look for the RDM button at the bottom right corner.

2.) Settings > Output Configuration (you have to select one of the DMX Ports (A, B, C, etc.) and switch from Out to RDM).

I can confirm it's working on 1.8.8.2 onPC and console.