So, https://www.openstreetmap.org/node/8001570417 is currently tagged with several names.

- name:en=Embassy of Cambodia
- name:fr=Ambassade du Cambodge
- official_name:en=Royal Embassy of Cambodia
- official_name:fr=Ambassade Royale du Cambodge

This means that depending on the map that you (or others) might use another name is shown, and the embassy should be found under all those names.

You write that the "OFFICIAL email address show[s]: "Ambassade - Mission permanente auprès des Nations Unies"", so is Cabodia/Cambodge *not* written there?

Meanwhile @Taktaal added `UN` in https://www.openstreetmap.org/changeset/179078550 and I added the phone number in https://www.openstreetmap.org/changeset/179088736