SUMMARY
With the aurorae decoration engine, close button requires two clicks to close the window.

STEPS TO REPRODUCE
1. Open any window/app. [System Settings --> Appearance --> Global Themes]
2. Click on something that will open a child/modal window. [Get New Global Themes...]
3. Close the child/modal window. Close "Get New Global Themes" window.
4. The System Settings window now requires two clicks to close.

OBSERVED RESULT
Once a child window is closed, the main window requires two clicks on the close button to close.

EXPECTED RESULT
Main window closes with a single click on the close button

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Neon (focal) / 5.23.90
KDE Plasma Version: 5.23.90
KDE Frameworks Version: 5.91.0
Qt Version: 5.15.3

ADDITIONAL INFORMATION
This behaviour is noticed in the "aurorae" decorations engine. Default Breeze decoration works fine.