问题描述：VS 2019升级到16.4.2后, .Net core一起被升级到了3.1，项目的目标框架也已改为3.1, 原来的项目打开后编译正常，调试正常。但启动发布到文件夹时出现了多个错误（这个生成配置是旧版一配置好的）。但内容都一样，提示Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore 3.1.0 和netcoreapp3.0 (.NETCoreApp,Version=v3.0)不兼容，还原失败。
解决方案：
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：项目文件夹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!
又测试了其他两个生成配置，界面显示都是3.1，保存后，实际文件并未更新，还是旧版的3.0，或者2.1