Internal insulation with udiin, experiences

Yes, of course there is condensate or moisture from the indoor air - via vapor pressure in the wall.

But a vapor barrier or vapor retarder, whether foil or liquid plastic, is simply deadly for an interior insulation that is fully glued, reinforced, and plastered, and has absolutely no place in this construction (regardless of the fact that it can't even be installed there).

You still owe the explanation....

Moisture can be absorbed and circulate in the insulation and adhesive layer of fully bonded interior insulation systems. Through vapor pressure equalization, the moisture can then be released back into the interior.

And these systems do not need a foil/retarder.

Otherwise, ventilation is also necessary (windows and doors open) so that excess moisture is transported outside in the end.

Well, the fact is that internal insulation on a detached house without monument protection is simply out of the question.

Because of a few cm of insulation, it won't get much darker now and you can enlarge the opening to the outside, as already suggested.

There are also highly efficient insulation solutions that add very little thickness, such as vacuum insulation panels. They are not cheap and not easy to install.

Just so you know: The insulation value of those Udiin things at that thickness is minimal. Even with just 2cm of mineral wool on the exterior wall, you get better insulation. If you still add a slim 100mm outside, you will already meet the Energy Saving Ordinance and achieve a massive improvement.

A few figures, calculated with a 36.5 cm Poroton wall from the 70s. U-value without insulation: 0.547 W/m²K U-value with your planned internal insulation: 0.463 W/m²K U-value with 10cm WLG 035 insulation: 0.213 W/m²K

Moisture can be absorbed and circulate in a fully adhered interior insulation system within the insulation and adhesive layers. And through vapor pressure equalization, the moisture can then be released back into the interior.

For this to work the way you imagine, you would need to regularly have very warm, dry air in the room. How do you do that? Why does moisture penetration of the insulation occur under these conditions at all? And what does this have to do with the (fully applied) adhesive?

... It is important in internal insulation that there are no cavities in the adhesive layer - condensate can then form there, which leads to mold.
….

@ Mr. Dr. Hix: Internal insulation is not exactly rocket science! And the insulation system that the OP wants to use does not need a barrier/retarder.