Winform that has many controls takes a long time to paint on mono

Label1.SuspendLayout();
Label1.Text = "new text here";
Label1.ResumeLayout();

public static class ControlsExtension
{
    // ref: https://stackoverflow.com/a/42389596
    public static void SetDoubleBuffered(this Control control, bool doubleBuffered = true)
    {
        control
            .GetType()
            .GetProperty("DoubleBuffered", System.Reflection.BindingFlags.Instance |
                                           System.Reflection.BindingFlags.NonPublic)
            ?.SetValue(control, doubleBuffered, null);
    }
}

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        this.Resize += Form1_Resize;

        // Canvas is a PictureBox control
        Canvas.Paint += Canvas_Paint;
        Canvas.MouseClick += Canvas_MouseClick;
 
        Canvas.SetDoubleBuffered();
        Canvas.BackColor = Color.Gray;
        Canvas.BorderStyle = BorderStyle.FixedSingle;
        Canvas.Cursor = Cursors.Hand;
    }

    private bool showCells = true;

    private record Cell(int Row, int Column, string Text, bool Visible = true);

    private readonly List<Cell> cells = new();

    private readonly float cellWidth = 50f;
    private readonly float cellHeight = 50f;
    private readonly Font cellFont =  new Font( "Time New Roman", 8, FontStyle.Bold );

    private readonly StringFormat cellTextFormat = new StringFormat()
    {
        LineAlignment = StringAlignment.Center,
        Alignment = StringAlignment.Center
    };

    private readonly Color cellBackColor = Color.White;
    private readonly Color cellForeColor = Color.Black;
    private readonly Color cellBorderColor = Color.Black;

    private void Form1_Resize(object? sender, EventArgs e)
    {
        //Canvas.Invalidate();
    }

    private void Canvas_MouseClick(object? sender, MouseEventArgs e)
    {
        if (showCells)
            labSelected.Text = $@"{Math.Floor(e.X / cellWidth):N0},{Math.Floor(e.Y / cellHeight):N0}";
    }

    private void Canvas_Paint(object? sender, PaintEventArgs e)
    {
        Graphics gr = e.Graphics;

        foreach (Cell cell in cells)
        {
            RectangleF rect = new RectangleF(cell.Column * cellWidth,
                                             cell.Row * cellHeight,
                                             cellWidth,
                                             cellHeight);
        
            // background
            using SolidBrush backBrush = new SolidBrush(cellBackColor);
            gr.FillRectangle(backBrush, rect);

            // are we hiding the cells?
            if (!showCells)
                continue;

            // border
            using Pen pen = new Pen(cellBorderColor, 1);
            pen.Alignment = PenAlignment.Outset;
            gr.DrawRectangle(pen, rect);

            // text
            using SolidBrush foreBrush = new SolidBrush(cellForeColor);
            gr.DrawString(cell.Text, cellFont, foreBrush, rect,
                         cellTextFormat);
        }
    }

    private void OnAddClick(object sender, EventArgs e)
    {
        cells.Clear();
        
        FillCells();

        showCells = true;
        Canvas.Invalidate();
    }

    private void OnShowClick(object sender, EventArgs e)
    {
        if (showCells) return;

        showCells = true;
        Canvas.Invalidate();
    }

    private void OnHideClick(object sender, EventArgs e)
    {
        if (!showCells) return;

        showCells = false;
        Canvas.Invalidate();

        labSelected.Text = "None";
    }

    void FillCells()
    {
        int nLabelNum = 10;

        for (int j = 0; j < nLabelNum; j++)
        for (int i = 0; i < nLabelNum; i++)
            cells.Add(new Cell(j, i, $"{i} | {j}"));
    }
}