問題描述：VS 2019升級到16.4.2后, .Net core一起被升級到了3.1，項目的目標框架也已改為3.1, 原來的項目打開后編譯正常，調試正常。但啟動發布到文件夾時出現了多個錯誤（這個生成配置是舊版一配置好的）。但內容都一樣，提示Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore 3.1.0 和netcoreapp3.0 (.NETCoreApp,Version=v3.0)不兼容，還原失敗。
解決方案：
same here when publishing:
Package Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore 3.1.0 is not compatible with netcoreapp3.0 (.NETCoreApp,Version=v3.0). Package Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore 3.1.0 supports: netcoreapp3.1 (.NETCoreApp,Version=v3.1)
Everything is set to 3.1 but...
when looking at publishprofiles FolderProfile.pubxml（文件位置：項目文件夾xxx\Properties\PublishProfiles） the TargetFramework is still set to 3.0 while going to the publish screen it shows 3.1 !!! and not 3.0 !! but the setting in the pubxml file is 3.0: <TargetFramework>netcoreapp3.0</TargetFramework>
I think the issue is in the publish profiles…
Changing it to netcoreapp3.1 in pubxml fixes everything!
又測試了其他兩個生成配置，界面顯示都是3.1，保存后，實際文件並未更新，還是舊版的3.0，或者2.1