Stone wall made of stone/stone slabs? Living room / kitchen

Both, the landlord has already been asked and is not cooperating. Therefore, that option is off the table. I had also seen the panels with adhesive sides, but at the same time heard that some of them have fallen off the walls again. So I think the panels with adhesive sides are not that optimal either. My last idea would therefore be to leave the wallpaper on and put the styrofoam panels on the wallpaper, since styrofoam seems to be the lightest.

Then I would first glue Smooth Fleece and on top of it what you like.

Then just go ahead and do it the way I suggested in #20. You can build the UK out of wood, attach it to the wall with a few screws, cover it with panels, and stick your Styrofoam on it. Don't make it more complicated than it is.

So, gluing a polystyrene board onto the current textured wallpaper is not recommended? (for me the easiest)

no, rather not. Better to drill a batten to the wall and then attach the cladding to it

What do you think of the glue (Universalkleber)? I am now unsure whether this glue can be easily removed afterwards?

link removed; Bauexperte