我们可以在.NET MAUI中使用Using Custom Renderers来删除多余的空间，并使图标垂直居中。
目前标题有一个固定的高度，所以在图标下面有一个空白的空间。我们需要使用Using Custom Renderers来设置bottomView.LabelVisibilityMode = LabelVisibilityMode.LabelVisibilityUnlabeled;，以删除标题占用的额外空间，并使图标垂直居中。
以下是详细步骤：
1.在应用程序的Platforms/Android/目录中创建一个自定义ShellRenderer类：

using Microsoft.Maui.Controls.Handlers.Compatibility; 
using Microsoft.Maui.Controls.Platform.Compatibility;

namespace MauiApp2;

class CustomShellHandler : ShellRenderer
{
    protected override IShellBottomNavViewAppearanceTracker CreateBottomNavViewAppearanceTracker(ShellItem shellItem)
    {
        return new Platforms.Android.CustomShellBottomNavViewAppearanceTracker(this, shellItem.CurrentItem);
    }

}

1.要自定义BottomNavView，请在同一目录下创建一个新类CustomBottomNavViewAppearanceTracker：

using Android.Graphics.Drawables; 
using Android.Views;
using Google.Android.Material.BottomNavigation;
using Microsoft.Maui.Controls.Platform;
using Microsoft.Maui.Controls.Platform.Compatibility;
using Microsoft.Maui.Platform;

namespace MauiApp2.Platforms.Android
{

    class CustomShellBottomNavViewAppearanceTracker : ShellBottomNavViewAppearanceTracker
    {
        private readonly IShellContext shellContext;

        public CustomShellBottomNavViewAppearanceTracker(IShellContext shellContext, ShellItem shellItem) : base(shellContext, shellItem)
        {
            this.shellContext = shellContext;
        }

        public override void SetAppearance(BottomNavigationView bottomView, IShellAppearanceElement appearance)
        {
            base.SetAppearance(bottomView, appearance);
         

            // the key is to set like below
            bottomView.LabelVisibilityMode = LabelVisibilityMode.LabelVisibilityUnlabeled;

        }

    }

}

1.最后一步是在MauiProgram.cs中注册我们的处理程序，如下所示：

var builder = MauiApp.CreateBuilder(); 
builder
    .UseMauiApp<App>()
    .ConfigureMauiHandlers(handlers =>
{
#if ANDROID
            handlers.AddHandler(typeof(Shell), typeof(CustomShellHandler));
#endif
 })

运行输出：