Where does Qt Creator save its settings?

See QtCreator Quick Tour.

Qt Creator creates the following files and directories:

QtCreator.db
QtCreator.ini
qtversion.xml
toolChains.xml
qtcreator
qtc-debugging-helper
qtc-qmldump

The location depends on the platform. On Linux and other Unix
platforms, the files are located in ~/.config/QtProject and
~/.local/share/data/QtProject/qtcreator.

On Mac OS, the files are located in ~/.config/QtProject and
~/Library/Application Support/QtProject/Qt Creator.

On Windows in general, the files are located in %APPDATA%\QtProject and %LOCALAPPDATA%\QtProject. Yes, you can use these paths in Explorer and in various command line shells. The environment variables (between the %-signs) are expanded automatically. If you need the concrete paths, see below.

On Windows 10, 8, Vista and 7, the files are located in
<drive>:\Users\<username>\AppData\Roaming\QtProject and
<drive>:\Users\<username>\AppData\Local\QtProject.

On Windows XP, the files are located in <drive>:\Documents and Settings\<username>\Application Data\QtProject and <drive>:\Documents and Settings\<username>\Local Settings\Application Data\QtProject.