Extend the partition by 10 cm - how should one do that?

Hello and welcome. I am new here and need your professional help.

Our friends (already somewhat older) have bought an already finished little house with underfloor heating. The older floor (laminate) has been removed, now there is a bare screed floor. A partition wall (not a load-bearing wall) is to be extended by 10 cm. The thickness/width of the wall is also 10 cm. The construction of the wall is described as "massive gypsum wall panels."

How can this extension be best done? I initially thought of wooden beams, but after some research, I found out that wood is too "flexible" and thus cracks can appear in the wall (especially in the transition area between the previous wall and the extension).

How would you do it? The extension should be stable and the transitions straight. Thank you very much!

Is the wall now a solid masonry wall or a stud wall (= clad with gypsum wallboards = drywall in common parlance or similar).

I would simply connect a drywall partition. Done correctly you won’t see anything, the wall will then be in the construction method in which the previous wall also is.

As far as I understand, with gypsum boards.

What is the best way to construct a drywall partition with a 10 cm extension?

Can't anyone help??

As far as I understand, with gypsum boards.

What is the best way to execute a drywall with a 10 cm extension?

Just like a 5 m long wall

Stud frame (metal or wood) and then plasterboard. Fill joints and corners (with edge protection, mesh tape, etc.).

Have you googled it already?