Not able to close Qt Creator Preferences window after changing the theme to dark mode

I opened Qt Creator, opened preference window to change the theme to dark. after changing the theme, I tried pressing apply button, ok button, cancel button and close button. Nothing was working. Window was not closing. Then using task manager, I was able to close the Qt.

Qt Version: 5.15.2

Qt Creator version: 8.0.2

I closed Qt from task manager.

This issue is observed only once.