"and broken the everlasting covenant" (24:5). Which covenant does it mean?

The verse doesn't say. It says what was done: "they have transgressed the laws, violated the statutes, and broken the everlasting covenant" (24:5), and what followed: "The earth also is polluted under its inhabitants" (24:5) and "Therefore the curse has devoured the earth" (24:6) (tap covenant, curse). In Hebrew everlasting covenant is berit olam, and the Hebrew Bible has the two words side by side 16 times: Genesis 9:16, 17:7, 17:13, 17:19, Exodus 31:16, Leviticus 24:8, 2 Samuel 23:5, 1 Chronicles 16:17, Psalm 105:10, Isaiah 24:5, 55:3, 61:8, Jeremiah 32:40, 50:5, Ezekiel 16:60 and 37:26. The WEB gives them as everlasting covenant in 15 and as "a perpetual covenant" in Exodus 31:16. They are said of "the everlasting covenant between God and every living creature of all flesh that is on the earth" (Genesis 9:16), of God's covenant with Abraham and his offspring (Genesis 17:7, 17:13, 17:19), confirmed "to Israel for an everlasting covenant" (Psalm 105:10; also 1 Chronicles 16:17), of the Sabbath (Exodus 31:16) and the bread set in order before the LORD every Sabbath (Leviticus 24:8), and of God's covenant with David (2 Samuel 23:5). In the prophets the LORD says, "I will make an everlasting covenant with you, even the sure mercies of David" (Isaiah 55:3), and the words stand again in Isaiah 61:8, Jeremiah 32:40, 50:5, Ezekiel 16:60 and 37:26. These are the places the words stand. Isaiah 24:5 names none of them, and these notes don't choose among them.