Hide Buttons in Form View

In a submitted Sales Order, you can see buttons like Update Items, Status. Also there are many options under 'Create' button.

Custom Script

You can write custom script as shown below to hide these buttons.

frappe.ui.form.on('Sales Order', {
    refresh(frm) {
        setTimeout(() => {
            frm.remove_custom_button('Update Items');
            frm.remove_custom_button('Close', 'Status');
            frm.remove_custom_button('Work Order', 'Make');
        }, 10);
    }
});