I installed the dotnet-runtime-30 snap as described in Installation using Snap on Ubuntu 18.04.
Then i copied an app that was published on Windows with dotnet publish -f netcoreapp3.0 -r linux-x64 --self-contained=false to the Ubuntu host.

I found no way to run the executable:

1. ./myexecutable failed with
   A fatal error occurred. The required library libhostfxr.so could not be found. If this is a self-contained application, that library should exist in [/home/philipp/publish/]. If this is a framework-dependent application, install the runtime in the global location [/usr/share/dotnet] or use the DOTNET_ROOT environment variable to specify the runtime location or register the runtime location in [/etc/dotnet/install_location].
2. dotnet-runtime-30.dotnet ./myexecutable failed with
   It was not possible to find any installed .NET Core SDKs Did you mean to run .NET Core SDK commands? Install a .NET Core SDK from: https://aka.ms/dotnet-download
3. dotnet-runtime-30.dotnet ./myexecutable.dll failed with
   Failed to create CoreCLR, HRESULT: 0x80070008

On the other hand it works when the runtime snap is mounted and dotnet in the mounted filesystem is called with ~/mountpoint/dotnet ./myexecutable.dll or when the sdk snap is used.