@Anonymous
I'm not entirely sure what you mean by the Items property is a string. Items properties are always tables. They may be tables of strings, but they cannot be just a string.
So, I will assume perhaps that you have a table of strings of emails and will proceed with that.
Your formula (for example) would be the following on the Items property of the dropdown:
ForAll(
["email1@domain.com", "email2@domain.com", "email3@domain.com"],
{Value: Office365Users.UserProfileV2(Value).displayname}
)
This would give you a dropdown with Display Names of the users. However, each selection would now be the Display Name only (dropdownx.Selected.Value will be a Display Name). If you still want the email address as well and simply want to display the name, then change formula to the following:
ForAll(
["email1@domain.com", "email2@domain.com", "email3@domain.com"],
{Value: Office365Users.UserProfileV2(Value).displayname},
Email: Value
)
Now dropdownx.Selected.Value will be the Display Name and dropdownx.Selected.Email will be the email.