There is a critical breaking change in .NET 5. Apps using WinRT with .NET Core 3.x will need to be rebuilt because won't run on .NET 5.0 as-is. 🙀
.NET 5 relies on C#/WinRT to WinRT<>.NET interop. There is no longer built-in WinRT interop support for consistency's sake.

— Miguel Ramos (@marbtweeting) August 25, 2020