Thanks for the input!
Hmm, the problem is that the old setup used an external motion sensor (NodeRed docker on my NAS with a Hue motion sensor triggering NodeRed to sending the screen on/off command on the MM Raspberry Pi setup via MMM-Remote-control).
Sounds Like I have to scrap the NodeRed/Motion-sensor-setup and modify my MM-setup and include a motion sensor in it…
Or, how would things behave if I have MM installed on the Raspberry and run it in client mode? Would a “screen off” call turn off the screen on the client or would it make no sense to it?