Problem with Application page doesn't appear in Project Visual Basic

I'm using Visual Studio 17.13.5 latest version and working with my project everything is good , suddenly I got for this error :

What I did for trying solve this problem :

1-Delete obj+bin folder and rebuild.
2-Changing   <HighDpiMode>false</HighDpiMode> in Application.myapp to true nothing helped.
3-Created a new project and copied the files and put in the new one.

Nothing helped me ! But I got some error also : Custom tool error: Failed to generate file: There is an error in XML document (11, 35).

So I'm confusing and can not find any solution !

If you set the High DPI mode via the project properties page (.NET Core 3.1+), you will see that the <HighDpiMode> entry takes numeric values between 0 and 4. There is a drop-down with available values.

E.g.:

<HighDpiMode>0</HighDpiMode>

There is a description of these modes in HighDpiMode Enum

First, delete the line <HighDpiMode>false</HighDpiMode>.

Then, in Visual Studio, right click on the VB Project in the Solution Explorer and search for the High DPI Mode:

Here you can select the desired mode and this will re-add the <HighDpiMode> line to the setting in a compatible way (and yes, it is a number, not a Boolean).

Update for .NET Framework 4.8

In a freshly created Windows Forms App using .NET Framework 4.8 my Application.myapp file looks like this:

<?xml version="1.0" encoding="utf-8"?>
<MyApplicationData xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <MySubMain>true</MySubMain>
  <MainForm>Form1</MainForm>
  <SingleInstance>false</SingleInstance>
  <ShutdownMode>0</ShutdownMode>
  <EnableVisualStyles>true</EnableVisualStyles>
  <AuthenticationMode>0</AuthenticationMode>
  <ApplicationType>0</ApplicationType>
  <SaveMySettingsOnExit>true</SaveMySettingsOnExit>
</MyApplicationData>

There is no HighDpiMode tag there. According to "High DPI support in Windows Forms" you can make changes to app.config.