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()) }
    }
}