Please help me understand a 1099 info from a foreign bank

Friend who is a US dual citizen has investments in his European country of birth (reported to the IRS, all legal). I am helping him with taxes. He is working with a large accounting firm, I am sort of "arms length" in this and don't have access to them for questions (and his cognitive decline also come into play here).

He received a report from his European bank that shows 1099 items, (total ordinary dividends, Qualified dividends, etc.) but format was not the typical ones you get from 1099 issuers, e.g., qualified dividends were line 3a NOT line 2b.

One section of this report was numbers all from US based investments--ETFs, some equities. And he received a 1099 from an affiliated US investment house that must work with his European bank that reported the same numbers as the foreign bank but in the "proper" 1099 format.

Separately there was a section of just non-US investments. (total ordinary dividends, Qualified dividends, etc.)

Question: necessary to report both categories -- US investments and non--to the IRS? Are the non-US investments held abroad taxable? If not, is this why the US investment house 1099 excludes the non-US based investment results? Thanks in advance.