The room of requirement canonically does not appear on the Marauder’s map. In fact the Marauder’s map has no reason to show the Chamber of Secret since if it is supposed to show only places that the Marauders know (I don’t remember what is the origin of the map in HPMOR though).
Harry speculates that the marauders stole part of the Hogwarts security system, but he’s not necessarily a reliable narrator.
Other fics imply that the map might have read-only access to the Hogwarts Wards/wardstone, in which case the Chamber would not have been there until the wards were adjusted to allow entry.
The room of requirement canonically does not appear on the Marauder’s map.
In fact the Marauder’s map has no reason to show the Chamber of Secret since if it is supposed to show only places that the Marauders know (I don’t remember what is the origin of the map in HPMOR though).
Harry speculates that the marauders stole part of the Hogwarts security system, but he’s not necessarily a reliable narrator.
Other fics imply that the map might have read-only access to the Hogwarts Wards/wardstone, in which case the Chamber would not have been there until the wards were adjusted to allow entry.