Hello @wonmin han ,
Welcome to Microsoft Q&A forum.
Please first try to reset Toolbox(right-click in Toolbox > Reset Toolbox) and check again.
Also, try to remove the control and then readd it to the Toolbox. Run devenv /ResetSettings in
Developer Command Prompt for Visual Studio 2022 to reset VS settings and repair VS from VS Installer > More > Repair.
If this issue persists, could you please share the detailed steps about how you added a user control to the Toolbox with us to reproduce this issue and check further?
Besides, did "Choose Toolbox Items" window show WPF Components correctly before you added the user control to the Toolbox?
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