How to determine that I have to make round corners (or not)?

Thank you for the link.

When I use the following method in the environment of the Windows 11 developer virtual machine, I receive DWM_WINDOW_CORNER_PREFERENCE.DWMWCP_DEFAULT. All windows of each app in that environment have not round corners. So DWM_WINDOW_CORNER_PREFERENCE.DWMWCP_DEFAULT doesn't help me to decide it. When all windows of each app have not round corners, I don't want to make round corners in my app too. Is there any other way to detect it?

public MainWindow()
{
	InitializeComponent();

	IntPtr	hWindow = new WindowInteropHelper(GetWindow(this)).EnsureHandle();
	bool?	ret = GetRoundCorners(hWindow);
}

internal static bool? GetRoundCorners(IntPtr hWnd)
{
	DWM_WINDOW_CORNER_PREFERENCE wcr = 0;

	int res = DwmGetWindowAttribute(hWnd, DWMWINDOWATTRIBUTE.DWMWA_WINDOW_CORNER_PREFERENCE, ref wcr, sizeof(DWMWINDOWATTRIBUTE));

	if (res != 0)
		return null;

	return wcr == DWM_WINDOW_CORNER_PREFERENCE.DWMWCP_ROUND || wcr == DWM_WINDOW_CORNER_PREFERENCE.DWMWCP_ROUNDSMALL;
}

As the doc says that apps are not rounded in a VM, you could test if you run in a VM

(some methods can be found from Google, like IsVirtualMachine at https://github.com/carlospolop/PEASS-ng/blob/f99387feed72eb9112e4916608bcc6da4888330c/winPEAS/winPEASexe/winPEAS/Info/SystemInfo/SystemInfo.cs#L21