There is a mod that adds simple dirt gravity with some tweaks, depending on world configuration: https://mods.vintagestory.at/show/mod/24289
I assume it does what I have done in my own custom mod, which is to add the gravity behavior from sand to soil using a patch:
[
{
"op": "add", "side": "Server",
"file": "game:blocktypes/soil/soil.json", "path": "/behaviors/-",
"value": { "name": "UnstableFalling", "properties": { "fallSound": "effect/rockslide", "dustIntensity": 1, "fallSidewaysChance": 0.5 } }
}
]
