.net standard compatibility - .net-core

Question

According to this page, .NET Core 2.1.15 is compatible with .NET standard 2.0. We have an application that had projects with the above versions and it worked, but when we loaded it again recently, we received the following error:
The current .NET SDK does not support targeting .NET Standard 2.0. Either target .NET Standard 1.6 or lower, or use a version of the .NET SDK that supports .NET Standard 2.0.
Our app MUST use SDK ver 2.1.803 (defined in global.json) and .net core 2.1.15 (Also specified in appsettings).
Here are my installed .net versions:
C:\Windows\system32>dotnet --info .NET Core SDK (reflecting any
global.json): Version: 2.2.109 Commit: 586f23c400
Runtime Environment: OS Name: Windows OS Version: 10.0.17134
OS Platform: Windows RID: win10-x64 Base Path: C:\Program
Files\dotnet\sdk\2.2.109\
Host (useful for support): Version: 2.2.7 Commit: b1e29ae826
.NET Core SDKs installed:
2.1.202 [C:\Program Files\dotnet\sdk]
2.1.505 [C:\Program Files\dotnet\sdk]
2.1.511 [C:\Program Files\dotnet\sdk]
2.1.803 [C:\Program Files\dotnet\sdk]
2.2.109 [C:\Program Files\dotnet\sdk]
.NET Core runtimes installed: Microsoft.AspNetCore.All 2.1.9
[C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.15 [C:\Program
Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.7 [C:\Program
Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.9 [C:\Program
Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.15 [C:\Program
Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.7 [C:\Program
Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.NETCore.App
2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.9 [C:\Program
Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App
2.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.2.7 [C:\Program
Files\dotnet\shared\Microsoft.NETCore.App]
To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download
We tried the following:
Uninstalled all .net core and sdk versions that were not 2.1.15 and 2.1.803 respectively,
Updated VS 2017 to the latest version
Downgraded to .NET Standard 1.6, but we had a lot of features that were not available to this version
Added .NET Standard nuget package back and updated all .NET Standard projects to use it, but received a similar message: SDK incompatibility.
So my questions are:
How do I know what .NET standard version is installed on my machine?
Did anyone experience this issue before?
Thanks
Alex

Answer 1

VS 2019 resolved the issue. It is the only IDE to work with .net Core 2.1.15 and SDK 2.1.803