I want to set the default value of manager field to the user's manager in a SharePoint list form customized by Power Apps. User and Manager are all Person type column in the SharePoint list.

I tried the formulas like:
Office365Users.ManagerV2(DataCardValue2.Selected.Email).displayName

f(!IsBlank(DataCardValue2.Selected.Email),
Office365Users.ManagerV2(DataCardValue2.Selected.Email).displayName,
""
)

If(!IsBlank(DataCardValue2.Selected.Email), Office365Users.ManagerV2(DataCardValue2.Selected.Email).displayName)
All returns errors. I am new to Power Apps and want to hear suggestions form you experts.