Here we find the repeating fraction (see also with 2 Kings 21:1–26): as did his father Manasseh, Amon did things of which the Lord strongly disapproved. There is a difference here with 2 Kings 21:1–26. Second Chronicles tells of the repentance of Manasseh, which we do not read about in 2 Kings. Manasseh is mentioned again here in 2 Kings 21:20 (“as his father Manasseh had done”), but Chronicles adds to this that Amon did not humble himself before the Lord, as his father Manasseh had humbled himself. Of course, the writer of 2 Kings cannot mention this, as he also does not mention the repentance of Manasseh.
20 And he did what was evil in the sight of the LORD, as Manasseh his father had done.