dotnet run x.csproj "... libhostfxr.dylib could not be found." - .net-6.0

Question

Running a .NET Core project on a Mac with .NET 6.0 installed causes a strange error.
lukepuplett#Lukes-Air > ~/Documents/Git/Repo/src/Corp.App.Mvc > > master ± > dotnet run Corp.App.Mvc.csproj
A fatal error occurred. The required library libhostfxr.dylib could not be found.
If this is a self-contained application, that library should exist in [/Users/lukepuplett/Documents/Git/Repo/src/Corp.App.Mvc/bin/Debug/net5.0/].
If this is a framework-dependent application, install the runtime in the global location [/usr/local/share/dotnet/x64] or use the DOTNET_ROOT environment variable to specify the runtime location or register the runtime location in [/etc/dotnet/install_location].
The .NET runtime can be found at:
- https://aka.ms/dotnet-core-applaunch?missing_runtime=true&arch=x64&rid=osx.11.1-x64&apphost_version=5.0.12
Note that the project builds fine.
macOS Monterey, Apple Silicon M1 and .NET 6.0 is installed.

Answer 1

This can occur when the project is targeting an older .NET Core version. The error is confusing because the project may build okay, and you'd expect a more accurate message.
A better message can be seen when executing the compiled binary directly, see below.
lukepuplett#Lukes-Air > ~/Documents/Git/Repo/src/Corp.App.Mvc/bin/Debug/net5.0 > > master ± > dotnet Corp.App.Mvc.dll
It was not possible to find any compatible framework version
The framework 'Microsoft.AspNetCore.App', version '5.0.0' (arm64) was not found.
- The following frameworks were found:
6.0.0 at [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
You can resolve the problem by installing the specified framework and/or SDK.
The specified framework can be found at:
- https://aka.ms/dotnet-core-applaunch?framework=Microsoft.AspNetCore.App&framework_version=5.0.0&arch=arm64&rid=osx.11.1-arm64
The problem can happen when you've pulled down code from a Git repo that is targeting .NET Core 5, for example.