Depending on the account type, foreign withholding taxes apply, and also depending on account type, some are recoverable, or a portion are recoverable.

Does the app already take this into account?

Yes. The app considers foreign witholding taxes for US investments in Non-Registered, TFSA, RESP and RDSP accounts. For Non-registered accounts the app considers the foreign tax credit that can be used to recover them.

Amazing!  Thank you!