11:4
“As Solomon grew old ...” God had warned that marrying foreign women would lead to one being led astray to worship other gods. As Solomon grew old , this happened. Solomon’s heart went after other gods, and he was no longer “fully devoted to the Lord”. David also sinned in the sexual area, (though not to the same extent as Solomon), but he never went in for idol worship.
11:5-8
Some of the false gods that Solomon went after are named. Molech was associated with child sacrifice. “So Solomon did evil in the eyes of the Lord”. The phrase “did evil in the eyes of the Lord” is one that will appear many times in 1 and 2 Kings. Solomon built high places for these “detestable” idols. He seems to have made offerings and sacrifices to the gods of all his wives. The text makes clear that these gods were “detestable”. Solomon was active in worshipping idols, building high places for the false gods.