I created Custom TabBar that has middle action button inside. For that, i set up this tabbar with empty space where i can render button:

Appshell

<custom:MiddleViewTabBar x:Name="MiddleViewTabBar" FlyoutItemIsVisible="False">
    ...
    <Tab Title="{Binding SomeTitle}" Icon="icon.png">
        <ShellContent Title="{Binding SomeTitle}" ContentTemplate="{DataTemplate something:SomePage}" Route="SomeRoute" />
    </Tab>
    <Tab>
        <ShellContent ContentTemplate="{DataTemplate accountOperations:AccountOperationAddPage}" Route="AddAccountOperation" />
    </Tab> // This is where i create empty space for button
    <Tab Title="{Binding AccountOperationsTitle}" Icon="ic_operations.png">
        ...
    </Tab>
    ...
</custom:MiddleViewTabBar>

I created CustomShellRenderer which looks same for iOS and Android handlers:

public class CustomShellHandler : ShellRenderer {
protected override IShellItemRenderer CreateShellItemRenderer(ShellItem shellItem) {
    return new MiddleShellItemRenderer(this);
}

ShellItemRenderer for iOS handler where i placed rendering item inside Grid:

public class MiddleShellItemRenderer : ShellItemRenderer {
    private UIView? _middleView;

    public MiddleShellItemRenderer(IShellContext context) : base(context) { }

    public override void ViewDidLoad() {
        base.ViewDidLoad();
        Shell.Current.PropertyChanged += UpdateMiddleViewVisibility;
    }

    private void UpdateMiddleViewVisibility(object? sender, System.ComponentModel.PropertyChangedEventArgs e) {
        if (_middleView is null || Shell.Current.CurrentPage is null) {
            return;
        }

        var tabBarIsVisible = Shell.GetTabBarIsVisible(Shell.Current.CurrentPage);
        _middleView.Hidden = !tabBarIsVisible;
    }

    public override async void ViewWillLayoutSubviews() {
        base.ViewWillLayoutSubviews();
        if (View is not null && ShellItem is MiddleViewTabBar tabBar) {
            if (_middleView is not null) {
                _middleView.RemoveFromSuperview();
            }

            if (_middleView is null) {
                var grid = new Grid() {
                    ColumnDefinitions = [
                        new ColumnDefinition { Width = GridLength.Star }
                    ],
                    RowDefinitions = [
                        new RowDefinition { Height = GridLength.Star }
                    ]
                };
                var middleViewSize = 50;
                var imageButton = new ImageButton {
                    Source = tabBar.MiddleViewIconSource,
                    Command = tabBar.MiddleViewCommand,
                    Margin = new Thickness(0),
                    Padding = new Thickness(0),
                    BackgroundColor = Colors.Green,
                    Aspect = Aspect.AspectFit
                };
                grid.Children.Add(imageButton);
                _middleView = grid.ToPlatform(App.Current.MainPage.Handler.MauiContext);
                _middleView.Frame = new CGRect(CGPoint.Empty, new CGSize(middleViewSize, middleViewSize));
                _middleView.AutoresizingMask = UIViewAutoresizing.FlexibleRightMargin | UIViewAutoresizing.FlexibleLeftMargin |
                                               UIViewAutoresizing.FlexibleBottomMargin; 
                _middleView.Layer.CornerRadius = _middleView.Frame.Width / 2;
                _middleView.Layer.MasksToBounds = false;
            }

            _middleView.Center = new CGPoint(View.Bounds.GetMidX(), TabBar.Frame.Top + 4 + _middleView.Frame.Height / 2);
            View.AddSubview(_middleView);
        }
    }
}

I tested this code in IPhone 15 and it look good:
https://imgur.com/a/W34PZfL but in IPhone SE i see some clipping because size is not adapting https://imgur.com/a/mUeZhuu. What im doing wrong?

Same problem is in Android