Computer Configuration > Administrative Templates > Google Chrome
Both
HKLM\Software\Policies\Google\Chrome
Specifies whether the user may open pages in Incognito mode in Google Chrome. If 'Enabled' is selected or the policy is left unset, pages may be opened in Incognito mode. If 'Disabled' is selected, pages may not be opened in Incognito mode. If 'Forced' is selected, pages may be opened ONLY in Incognito mode. Note that 'Forced' does not work for Android-on-Chrome Note: On iOS, if the policy is changed during a session, it will only take effect on relaunch.