Remove Cursor from TextBox C#

Well, I have managed it somehow with the code that I have put in the comment .

In the class Formthat implements those controls TextBox, you do the following:

1. You do using System.Runtime.InteropServices;at the beginning of the file MiForm.cs (Where MiFormis the name of the code file corresponding to the Formone you use.)

2. You define the external method HideCaret:

   [DllImport("user32.dll")]
   static extern bool HideCaret(IntPtr hWnd);

Then for each TextBoxyou configure the event GotFocusas follows:

foreach (TextBox item in MiColeccionDeTextBoxes) {
    item.GotFocus += delegate { HideCaret(item.Handle); }
}

And with that you have what you need to complete the Form, below I leave all the code of one Form1.csthat I made while I was trying:

// Recuerda el using System.Runtime.InteropServices;

public partial class Form1 : Form
{
    [DllImport("user32.dll")]
    static extern bool HideCaret(IntPtr hWnd);

    public Form1()
    {
        InitializeComponent();
        TextBox[] texts = { txt1, txt2 };
        foreach (TextBox item in texts)
            item.GotFocus += delegate { HideCaret(item.Handle);  };
    }

    /// <summary>
    /// Required designer variable.
    /// </summary>
    private System.ComponentModel.IContainer components = null;

    /// <summary>
    /// Clean up any resources being used.
    /// </summary>
    /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
    protected override void Dispose(bool disposing)
    {
        if (disposing && (components != null)) {
            components.Dispose();
        }
        base.Dispose(disposing);
    }

    #region Windows Form Designer generated code

    /// <summary>
    /// Required method for Designer support - do not modify
    /// the contents of this method with the code editor.
    /// </summary>
    private void InitializeComponent()
    {
        this.txt1 = new System.Windows.Forms.TextBox();
        this.txt2 = new System.Windows.Forms.TextBox();
        this.SuspendLayout();
        // 
        // txt1
        // 
        this.txt1.Location = new System.Drawing.Point(12, 48);
        this.txt1.MaxLength = 1;
        this.txt1.Name = "txt1";
        this.txt1.Size = new System.Drawing.Size(100, 20);
        this.txt1.TabIndex = 0;
        // 
        // txt2
        // 
        this.txt2.Location = new System.Drawing.Point(12, 74);
        this.txt2.MaxLength = 1;
        this.txt2.Name = "txt2";
        this.txt2.Size = new System.Drawing.Size(100, 20);
        this.txt2.TabIndex = 1;
        // 
        // Form1
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
        this.ClientSize = new System.Drawing.Size(284, 261);
        this.Controls.Add(this.txt2);
        this.Controls.Add(this.txt1);
        this.Name = "Form1";
        this.Text = "Test Focus";
        this.ResumeLayout(false);
        this.PerformLayout();

    }

    #endregion

    private System.Windows.Forms.TextBox txt1;
    private System.Windows.Forms.TextBox txt2;
}

I would advise you not to use a TextBox to represent each square, you could use a picturebox and draw the number

How to draw text on picturebox?

Drawing Graphics in C Sharp

in this way you will have the events but you control the actions, it will not be as direct as assigning the .Text, but you will not have any cursor on the control

To make the assignment of the number simpler if you don't want to use the Paint event, you could see if with

Graphics g = pictureBox1.CreateGraphics();

or maybe something like

Bitmap bm = new Bitmap(pictureBox1.Width, pictureBox1.Height);

using (Graphics g = Graphics.FromImage(bm))
{
    using (SolidBrush myBrush = new SolidBrush(Color.Black))
    {
        using (Font myFont = new Font("Times New Roman", 24))
        {
            g.DrawString("aqui numero", myFont, myBrush, 10, 10);
            pictureBox1.Image = bm;
        }
    }
}

when you want to show a number you draw it in an image and assign it to the picturebox, if you need to assign a background color you can always do it without problems