Computer Configuration > Administrative Templates > Microsoft Edge
Both
HKLM\Software\Policies\Microsoft\Edge
Specifies whether the user can open pages in InPrivate mode in Microsoft Edge. If you don't configure this policy or set it to 'Enabled', users can open pages in InPrivate mode. Set this policy to 'Disabled' to stop users from using InPrivate mode. Set this policy to 'Forced' to always use InPrivate mode. Policy options mapping: * Enabled (0) = InPrivate mode available * Disabled (1) = InPrivate mode disabled * Forced (2) = InPrivate mode forced Use the preceding information when configuring this policy.