Good day to you all. I had the same problems. Various other characters, such as the question mark, were also wrong. The employee in the Digitec shop couldn't solve the problem straight away either. She searched for the problem in a forum. If I remember correctly, the physical keyboard does not have to be set to German(CH), but you have to scroll down further and select Swiss German. In any case, the keyboard has been working perfectly since then.

Greetings Marcel

Attention, the setting of the physical keyboard must be changed, not the setting of the on-screen keyboard. Under General Administration there is the entry "Physical Keyboard". There you can select the layout (e.g. Swiss German, Qwertz style). Then the special characters fit :)

This is possible in the Keyboard menu under Settings of your Galaxy Tab. Settings -> General Management -> Samsung Keyboard Settings -> Languages and Types -> Manage input settings.
I have used German (CH).

After that you can change the language with the "Lang" key.