如何在Net5中读取配置文件?

我使用Vb.net,FW:Net5

这是我的app.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
   <appSettings>
    <add key="ConnectString" value="DB/Sample.db3" />
  </appSettings>
    <system.diagnostics>
        <sources>
            <!-- This section defines the logging configuration for My.Application.Log -->
            <source name="DefaultSource" switchName="DefaultSwitch">
                <listeners>
                    <add name="FileLog"/>
                    <!-- Uncomment the below section to write to the Application Event Log -->
                    <!--<add name="EventLog"/>-->
                </listeners>
            </source>
        </sources>
        <switches>
            <add name="DefaultSwitch" value="Information" />
        </switches>
        <sharedListeners>
            <add name="FileLog"
                 type="Microsoft.VisualBasic.Logging.FileLogTraceListener, Microsoft.VisualBasic, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" 
                 initializeData="FileLogWriter"/>
            <!-- Uncomment the below section and replace APPLICATION_NAME with the name of your application to write to the Application Event Log -->
            <!--<add name="EventLog" type="System.Diagnostics.EventLogTraceListener" initializeData="APPLICATION_NAME"/> -->
        </sharedListeners>
    </system.diagnostics>
</configuration>

"System.Configuration.ConfigurationManager" 来自Nuget

我已经尝试将配置设置为:

Dim str = System.Configuration.ConfigurationManager.AppSettings("ConnectString")

但出现异常错误:

Configuration system failed to initialize

如何在vbnet5中读取app.config?