Built-in Data Maps
NeoForge provides a few data maps that mostly replace hardcoded in-code vanilla maps.
These data maps can be found in NeoForgeDataMaps, and are always optional to ensure compatibility with vanilla clients.
neoforge:compostables
NeoForge provides a data map that allows configuring composter values, as a replacement for ComposterBlock#COMPOSTABLES (which is now ignored).
This data map is located at neoforge/data_maps/item/compostables.json and its objects have the following structure:
{
    // A 0 to 1 (inclusive) float representing the chance that the item will update the level of the composter
    "chance": 1
}
Example:
{
    "values": {
        // Give acacia logs a 50% chance that they will fill a composter
        "minecraft:acacia_log": {
            "chance": 0.5
        }
    }
}