Probate Plus will not work out how much Inheritance Tax is due to be paid. But you can record the amount due and paid out within the system.
Calculating the amount of IHT due involves reference to some information outside of the knowledge of Probate Plus. Once you know the IHT bill amount you can enter it into the system.
If all beneficiaries pay a share of the IHT then you can enter the amount payable as an 'admin expense' within Probate Plus and show where the money is eventually paid from.
If some beneficiaries are exempt from paying IHT, then see this article for details of how to handle the IHT allocation in PPv5:
or (for Version 4)