Insulating a mortared roof

Hello, I have a question for you. As the title already says, I have a mortar-covered roof. Now I want to insulate it. My original plan was to install a provisional underlayment membrane between the rafters and lead it out at the last row of tiles. Inside, I wanted to use a climate membrane so that moisture could also be released into the interior. A roofer friend said I don’t need that because the roof is mortared; he says to double up the insulation up to the tiles, then the climate membrane, and that’s fine. (Before that, he wants to re-mortar any damaged areas in the mortar.) Now I have several concerns. On the one hand, if moisture gets into the insulation, it would have no way to dry out, right? Or can moisture also be released to the outside through the tiles? Would it be better to create ventilation? And if so, what would that look like? What would be your opinion on the right approach?

I wanted to attach another picture but somehow I can no longer edit the post. So here is another picture (The tensioned track there was still from the previous owner, it was not guided outward at the bottom. Previous structure, from outside to inside, was the visible track, wood fiberboard, insulation (very thin maybe 10cm) then Styrofoam (3cm), OSB. It was only one half of a roof)