Modernstone Cladding Experiences

Are there any pictures of that?

I'll do some tonight.

What was the back panel mounted on then?

Stable substructure (60x40 battens)
OSB boards (25mm)
Slate tiles (1-2mm thick) - simply with tile adhesive
Wiring behind the panel (power, HDMI, network)
The OSB slightly overhangs at the edge (can be seen quite well in picture three), as far as the strip for the LED strips is
The slate tiles also slightly overhang, so that thin strips can be glued on the side and thus nothing of the substructure can be seen anymore (of course, you can still reach the strip for the LEDs).

Color and brightness are of course freely adjustable (looks very bright here, but that's due to the photo). You can also (via an additional sensor) adjust the color to the TV program, control it via Alexa or similar, etc. Common LED strip technology.