我不认为你可以用BottomNavigationItem来完成它。合成的材料设计库遵循材料设计规范，正如你在这里看到的。
但是你不需要使用BottomNavigationItem来显示BottomAppBar中的项。你可以使用任何可组合的，如下所示：

Column(
    horizontalAlignment = Alignment.CenterHorizontally,
    modifier = Modifier
        .weight(1f)
        .clickable {
            navController.navigate(navItem.route)
        }) {
    val color =
        if (currentRoute == navItem.route) 
            LocalContentColor.current 
        else 
            LocalContentColor.current.copy(alpha = ContentAlpha.medium)
    Icon(
        painter = painterResource(id = navItem.icon), 
        navItem.label, 
        tint = color
    )
    // Set the space that you want...
    Spacer(modifier = Modifier.height(4.dp))
    Text(text = navItem.label, color = color, fontSize = 12.sp)
}

然而，正如我上面提到的，该库遵循材料设计规范，该规范将BottomAppBar的高度定义为56dp。因此，如果您想要更多定制的东西，您需要自己定制（例如，使用Row）。

我设法在图标和标签之间添加了填充。事实上，当我开始尝试这个方法时，我是将填充应用于文本/标签而不是图标，但是如果我们将填充应用于图标，就可以应用该间距。只需在图标上添加一个Modifier.padding(bottom = YOURDP)，它就可以工作了。
我认为这是可能的，因为在分析Material Design代码以应用Label with Icon之后，它应用了Label relative to Icon（你可以在下面的方法中看到），考虑到现有的空间，所以如果我们增加Icon占用的空间，它将使标签更低。

/**
 * Places the provided [labelPlaceable] and [iconPlaceable] in the correct position, depending on
 * [iconPositionAnimationProgress].
 *
 * When [iconPositionAnimationProgress] is 0, [iconPlaceable] will be placed in the center, as with
 * [placeIcon], and [labelPlaceable] will not be shown.
 *
 * When [iconPositionAnimationProgress] is 1, [iconPlaceable] will be placed near the top of item,
 * and [labelPlaceable] will be placed at the bottom of the item, according to the spec.
 *
 * When [iconPositionAnimationProgress] is animating between these values, [iconPlaceable] will be
 * placed at an interpolated position between its centered position and final resting position.
 *
 * @param labelPlaceable text label placeable inside this item
 * @param iconPlaceable icon placeable inside this item
 * @param constraints constraints of the item
 * @param iconPositionAnimationProgress the progress of the icon position animation, where 0
 * represents centered icon and no label, and 1 represents top aligned icon with label.
 * Values between 0 and 1 interpolate the icon position so we can smoothly move the icon.
 */
private fun MeasureScope.placeLabelAndIcon(
    labelPlaceable: Placeable,
    iconPlaceable: Placeable,
    constraints: Constraints,
    /*@FloatRange(from = 0.0, to = 1.0)*/
    iconPositionAnimationProgress: Float
): MeasureResult {
    val height = constraints.maxHeight

    // TODO: consider multiple lines of text here, not really supported by spec but we should
    // have a better strategy than overlapping the icon and label
    val baseline = labelPlaceable[LastBaseline]

    val baselineOffset = CombinedItemTextBaseline.roundToPx()

    // Label should be [baselineOffset] from the bottom
    val labelY = height - baseline - baselineOffset

    val unselectedIconY = (height - iconPlaceable.height) / 2

    // Icon should be [baselineOffset] from the text baseline, which is itself
    // [baselineOffset] from the bottom
    val selectedIconY = height - (baselineOffset * 2) - iconPlaceable.height

    val containerWidth = max(labelPlaceable.width, iconPlaceable.width)

    val labelX = (containerWidth - labelPlaceable.width) / 2
    val iconX = (containerWidth - iconPlaceable.width) / 2

    // How far the icon needs to move between unselected and selected states
    val iconDistance = unselectedIconY - selectedIconY

    // When selected the icon is above the unselected position, so we will animate moving
    // downwards from the selected state, so when progress is 1, the total distance is 0, and we
    // are at the selected state.
    val offset = (iconDistance * (1 - iconPositionAnimationProgress)).roundToInt()

    return layout(containerWidth, height) {
        if (iconPositionAnimationProgress != 0f) {
            labelPlaceable.placeRelative(labelX, labelY + offset)
        }
        iconPlaceable.placeRelative(iconX, selectedIconY + offset)
    }
}