Omnisharp fail I solved in this way
Note about using .NET Core 3.1.40x SDKs
The .NET 3.1.40x SDKs require version 16.7 of MSBuild.
For MacOS and Linux users who have Mono installed, this means you will need to set omnisharp.useGlobalMono to never until a version of Mono ships with MSBuild 16.7