Application Settings in .Net Core (WPF) and single exe - wpf

Question

To migrate an application I want to continue using the plain old settings that still come along with .Net5 (App.Config, Settings.settings and so on).
I need a simple built in solution without additional dependencies.
The proposed way seems to be appsettings.json or similar.
For that to use with WPF you need to add some additonal dependencies which bloat the project when
publishing it as single exe (not self contained). It is over-the-top for simple applications.
I followed the steps here:
Equivalent to UserSettings / ApplicationSettings in WPF dotnet core
The accepted answer from Alexander works for a normal exe built.
These are the generated files
MyApp.dll
MyApp.dll.config
MyApp.exe
Modifying "MyApp.dll.config" with an editor directly reflects the changed data in the code.
MessageBox.Show(Settings.Default.SomeConfigValue);
The used config file can be displayed using
var config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
MessageBox.Show(config.FilePath);
It displays
C:\Projekte\MyApp\MyApp\bin\Debug\net5.0-windows\MyApp.dll.config
Unfortunately this fails for single exe
These are the generated files (in publish folder)
MyApp.dll.config
MyApp.exe
Modifying "MyApp.dll.config" or "MyApp.exe.config" has no effect. The file does not seem to be used by the framework.
Above messagebox now shows
C:\Projekte\MyApp\Publish<Unknown>.config
How to get the built-in configuration system work with single exe?