LazyGridItemScope

fun Modifier.animateItem(
    fadeInSpec: FiniteAnimationSpec<Float>? = spring(stiffness = Spring.StiffnessMediumLow),
    placementSpec: FiniteAnimationSpec<IntOffset>? = spring(
            stiffness = Spring.StiffnessMediumLow,
            visibilityThreshold = IntOffset.VisibilityThreshold
        ),
    fadeOutSpec: FiniteAnimationSpec<Float>? = spring(stiffness = Spring.StiffnessMediumLow)
): Modifier

This modifier animates the item appearance (fade in), disappearance (fade out) and placement changes (such as an item reordering).

You should also provide a key via LazyGridScope.item/LazyGridScope.items for this modifier to enable animations.

import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.lazy.grid.GridCells
import androidx.compose.foundation.lazy.grid.LazyVerticalGrid
import androidx.compose.foundation.lazy.grid.items
import androidx.compose.material.Button
import androidx.compose.material.Text
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier

var list by remember { mutableStateOf(listOf("A", "B", "C")) }
Column {
    Button(onClick = { list = list + "D" }) {
        Text("Add new item")
    }
    Button(onClick = { list = list.shuffled() }) {
        Text("Shuffle")
    }
    LazyVerticalGrid(columns = GridCells.Fixed(1)) {
        items(list, key = { it }) {
            Text("Item $it", Modifier.animateItem())
        }
    }
}

@ExperimentalFoundationApi
open fun Modifier.animateItemPlacement(
    animationSpec: FiniteAnimationSpec<IntOffset> = spring(
            stiffness = Spring.StiffnessMediumLow,
            visibilityThreshold = IntOffset.VisibilityThreshold
        )
): Modifier

This modifier animates the item placement within the Lazy grid.

When you provide a key via LazyGridScope.item/LazyGridScope.items this modifier will enable item reordering animations. Aside from item reordering all other position changes caused by events like arrangement changes will also be animated.