Should the ceiling under the attic be insulated?

Reed mats on the ceiling actually only served as plaster carriers, not as insulation.

I seem to remember that insulation applied in the wrong place can lead to mold. Walls and windows in old buildings must be considered together. Nowadays, insulation is applied on the outside. Hence also my objection to the ceiling, so that a cold roof is created.

The ceilings in the interior rooms were originally insulated with reed. We removed that. Now the ceilings are basically completely "naked"....only the concrete blocks can be seen. We want to then cover the ceilings with drywall and had considered insulating the cavity between the ceiling and the drywall.

As you have probably noticed by now, your wording was unfortunate in that it does not make clear what you are actually talking about: a) the paving stones as impact sound insulation on a wooden beam ceiling or b) the view from below of a precast concrete element ceiling. It has since become clearer that the latter is meant. But if it is, as I suspect, then it would most likely be a pumice concrete precast ceiling (with what kind of support beams it rests on?); battens should be easy to anchor for the drywall cladding there; in classic concrete that would be more difficult. Consider using this substructure as an installation level and, if necessary, recessing spotlights (or, for example, speakers in the kitchen) there.

In general, I recommend that you enliven the discussion with pictures of what you are talking about.

Not that you have to take his work as a standard, but I recommend as reading tip to check out the story of :

Doesn't change anything at all.. Just put on the insulation and that's it. Any moisture that may occur can escape through the stone wool.

Thank you for the many answers. It definitely helped us. We will not insulate the ceilings, but the attic. That this reed was only used so that the plaster holds was also not clear to us.
Best regards