How do I disable form resizing for users? [duplicate]

Change the FormBorderStyle to one of the fixed values: FixedSingle, Fixed3D,
FixedDialog or FixedToolWindow.

The FormBorderStyle property is under the Appearance category.

Or check this:

// Define the border style of the form to a dialog box.
form1.FormBorderStyle = FormBorderStyle.FixedDialog;

// Set the MaximizeBox to false to remove the maximize box.
form1.MaximizeBox = false;

// Set the MinimizeBox to false to remove the minimize box.
form1.MinimizeBox = false;

// Set the start position of the form to the center of the screen.
form1.StartPosition = FormStartPosition.CenterScreen;

// Display the form as a modal dialog box.
form1.ShowDialog();