The wall panels are above all inhomogeneous: the larger part of the wall surface is "hollow" in the load-bearing sense (filled with light fiber mats). For this, there are special toggle bolts. In between, usually at a 62.5 cm grid spacing, the vertical construction timbers run "behind". That means the bolt first grips into drywall (as it otherwise would in plaster) and then into wood (as it otherwise would in stone). There are also devices similar to detectors for power lines, but for beams.
Moisture barriers are not known to me as a topic for pure interior walls. How far under the drywall there is still a (kind of) chipboard must be asked from the manufacturer (who can also say where the timbers run, by the way, and I would always have the execution drawings of my house given to me), and it can vary. Even with timber frame construction, not all interior walls are equally strong. Essentially, there are three types of interior walls: ordinary purely room-dividing walls, partly as known from solid construction in two thicknesses (where quite possibly one of them can be without and one with a fiberboard layer under the drywall), and such walls that are simultaneously installation walls (where kitchens and bathrooms adjoin). For the latter, I would possibly expect moisture barriers on the wet room side.
Interior sides of exterior walls are a different matter than pure interior walls, as are interior walls that transition into exterior walls, for example where covered open spaces are integrated into the floor plan. The manufacturer can provide detailed information about where walls of which construction are located (and you should definitely have this information given to you).
In any case, you need not fear that your wall will rot away from indoor humidity where you have drilled a screw hole for a wall clock.