Thank you for your help.
I want to control the display method of the item list (④ of the attached image) of Outlook 2016 by GPO, but I asked a question because the setting value was not found.
On the Outlook screen, you can select "none", "1 line", "2 lines", "3 lines" for preview of the email body by "View"> "Preview message".
Is there a way to centrally manage this setting in AD using GPO?
It may be controlled by the registry.
Sorry to trouble you, but thank you for your response.