Isolated property is supposed to enable referencing in-process COM servers as a registration free COM dependency, but something got broken on the way: Visual Studio 2019 Preview and .NET 5 produce applications that lose the link.
It is still preview so hopefully things get resolved timely.
- The issue on GitHub: Single-File Executable Cannot Use Registration Free COM Interop in .NET 5-Preview 7
- My reproducer and my workaround
The reproducer itself is a nice template for checking out C#/C++ COM interop.