<PackageReference Include="System.Configuration.ConfigurationManager" Version="8.0.0-rc.1.23419.4" />

ConfigurationSaveMode

public enum ConfigurationSaveMode
Determines which properties are written out to a configuration file.
Full = 2

Causes all properties to be written to the configuration file. This is useful mostly for creating information configuration files or moving configuration values from one machine to another.

Minimal = 1

Causes only properties that differ from inherited values to be written to the configuration file.

Causes only modified properties to be written to the configuration file, even when the value is the same as the inherited value.