@hiranfilho
You can try to send the name to Flow then search for user, get first value, then get Email address and return it to PowerApps.
If you want this done quickly from Power Automate (Formerly Microsoft Flow) there is a convenient Flow Action for this called "Office 365 - Search for users" - you can find it by typing Office 365 or Search for users when looking for Flow actions after clicking "New Step".

You would feed the PowerApps input here instead of "John" - yes it will search the name, and a variety of other pieces automatically.
Note, this returns multiple values. After you get the user, if you want only the first user, get the first user using a Compose action.
Some people use an Apply To Each even if there's only one - we prefer to get the first directly. However it requires you to know exactly how to do this. Use this example - new Compose Action after the aformentioned action, with something like:
body('Search_for_users')?[0]
in this case.
Or, if you do need to email a potential match of multiple users, even better - then use an apply to each.
In your case though, you may only need one user, so the first match would work.
Even if you limit the number of returned results to one, the type returned is an Array, so either an Apply to Each should be used, or our preferred way
body('Search_for_users')?[0]
to get only the first value in cases where it is known only the first value is desired.