You're going to need a DataView with System.User in it and just show the Name attribute in a label. Then use a microflow as source and just pass back the $currentUser variable.
If you want to display an attribute of an inherited entity like the default Administration.Account with the FullName attribute, you'll have to retrieve the relevant entity in a retrieve action with a constraint like [id = $currentUser]
and take into account that not all users may be of that inherited type.