John Gill Commentary 2 Kings 23:9

"Nevertheless the priests of the high places came not up to the altar of Jehovah in Jerusalem, but they did eat unleavened bread among their brethren." — 2 Kings 23:9 (ASV)

Nevertheless, the priests of the high places came not up to the
altar of the Lord at Jerusalem
To sacrifice there, as the Targum; though they were removed from the high places, they were not admitted to officiate at the altar of the Lord, having offered in forbidden places:

but they did eat of the unleavened bread with their brethren ;
the priests that were pure, as the sons of Zadok; though they might not offer sacrifices, they were allowed to partake of the holy things with the priests, as the meat offerings made of flour unleavened, (Leviticus 2:4Leviticus 2:5) which are here meant, and put for all the rest on which the priests lived, see (Ezekiel 44:10–15) .