Computer Configuration > Administrative Templates > Google Chrome
Both
HKLM\Software\Policies\Google\Chrome
Setting the policy to Enabled means Google Chrome enforces guest sessions and prevents profile sign-ins. Guest sign-ins are Google Chrome profiles where windows are in Incognito mode. Setting the policy to Disabled, leaving it unset, or disabling browser Guest mode (through BrowserGuestModeEnabled) allows the use of new and existing profiles.