If this nonsense is really all about IPP status, then, turning this on its head, Charles is the one with Internationally Protected Person (IPP) status as Head of State. This extends to his immediate household, and to those who directly represent him in his HoS role.
It also brings Charles, and his immediate household, and those who represent him, certain protections from hostile actions.
The UN Convention Articles (notably Article 2.3) should be spelled out to Harry in single syllable soundbites if necessary. Harry is now NOT an IPP as he is neither a member of a Head of State's household nor does he represent a Head of State.
Harry perhaps needs to look closely at that passage in the Convention Article 2.3 on 'attacks on the person, freedom or dignity' of actual IPPs; not least while he is simultaneously slagging off Constitutional freedom of expression (his one defence) in the US.
https://treaties.un.org/doc/db/Terrorism/english-18-7.pdf