The netcore-2.2 reference set consists of the shared framework's facade
assemblies split across many files, and vbc only binds special types
like System.Void from an assembly that defines them rather than
following type forwards, so without an implicit SDK it needs the same
reference list as the C# side. The VB runtime must come from the legacy
reference set: before .NET Core 3.0 there is no
Microsoft.VisualBasic.Core.dll and the core build of the VB runtime is
a trimmed-down subset (no UBound etc.). Referencing the target
framework's own Microsoft.VisualBasic facade alongside that -vbruntime
choice is a BC32210 identity conflict, so it is dropped from both the
default reference list and the ReferenceVisualBasic flag handling.
All of this applies only where vbc runs without its implicit desktop
SDK path, i.e. off Windows; on Windows vbc.exe keeps the plain
reference list that already worked.
Assisted-by: Claude:claude-fable-5:Claude Code
Siegfried Pammer