How to attach to Kloasong wall/reed wall

[aabbcc]

Old apartment from 1919, apart from two walls that were redone with plywood+gypsum, the rest are kloassong walls consisting of

*about 2cm plaster
*reed mat
*horizontal planks
*studs? Behind these studs come the neighbor's studs for their inner wall.

How is it best to attach to these walls? Thinking of both lighter pictures up to heavier bookshelves/TV. The plaster crumbles just by looking at it. Is it enough with just a sufficiently long screw like 70mm that you drill straight into the plaster or should you use plugs as well? Unfortunately, there are quite large gaps between the planks

Behind an added inner wall that is now removed (studs+gypsum), there were two door openings from before the apartment was sectioned off. Here the builders filled in with gypsum, I think, how do you attach there as there are no planks behind?

 

[BirgitS]

Shine in between the lying boards and try to take pictures to find out if it's studs or something else.

Using wood screws in boards provides a very good fastening. In old houses, it might be best to do as they did when they were new, i.e., have floor-standing bookshelves, etc.

In drywall with a hollow space behind, you can use molly plugs for larger loads.

 

[aabbcc]

Shine a light between the horizontal boards and try to take photos to find out if they are studs or something else.

Screwing into boards with wood screws provides very good anchoring. In old houses, it might be best to do as they did when they were new, i.e., have floor-standing bookshelves, etc.

In drywall with a hollow space behind, you can use molly bolts for heavier loads.

Thanks! Unfortunately, the walls are painted now, but I guess I'll have to drill a test hole and see if I get a hold with a long screw. I'll have to get some molly bolts for the parts of the wall that are drywalled.