Hello @Ismail Yüksel Kuşoğlu,
Welcome to Microsoft Q&A forum.
In short: In white/empty space(in Toolbox), right-click => cancel the selection for "Show All" option. After that try to expand other categories.
Explanation: You can see those controls, because all the controls are shown("Show All" option has been selected). You cannot use them, because they are not compatible with the project type that you are using.
For example, you are developing a Windows Forms project, but all the controls are shown in the Toolbox, including the controls for WPF project, for C++ MFC project… but only controls which supports Windows Forms project are available.
One thing to note is that before you try to use the controls in Toolbox, please open the designer view first(for example, right-click the Form1.cs file > View Designer), otherwise you will see following error message in Toolbox.
If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.