Unable to run with .NET 6

[C1A551F13D]

I followed the instructions for building and running from source here: README.md. The only major deviation is the build machine already has .NET 5 SDK, but defaults to .NET 6.

$ dotnet --info
.NET SDK (reflecting any global.json):
 Version:   6.0.302
 Commit:    c857713418

Runtime Environment:
 OS Name:     linuxmint
 OS Version:  20.2
 OS Platform: Linux
 RID:         linux-x64
 Base Path:   /usr/share/dotnet/sdk/6.0.302/

global.json file:
  Not found

Host:
  Version:      6.0.7
  Architecture: x64
  Commit:       0ec02c8c96

.NET SDKs installed:
  2.2.402 [/usr/share/dotnet/sdk]
  3.0.103 [/usr/share/dotnet/sdk]
  3.1.421 [/usr/share/dotnet/sdk]
  5.0.408 [/usr/share/dotnet/sdk]
  6.0.300 [/usr/share/dotnet/sdk]
  6.0.302 [/usr/share/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.All 2.2.8 [/usr/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.2.8 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.3 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.27 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.17 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.7 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.2.8 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.3 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.27 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.17 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.7 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

Download .NET:
  https://aka.ms/dotnet-download

Learn about .NET Runtimes and SDKs:
  https://aka.ms/dotnet/runtimes-sdk-info

As you can see above, I have the .NET 5.0 SDK; however, when I run AvalonStudio:

~/projects/AvalonStudio/AvalonStudio/AvalonStudio/bin/Debug/net5.0$ ./AvalonStudio

I receive this error in the XAML preview window:

Unhandled exception. System.IO.FileLoadException: Could not load file or assembly 'System.Runtime, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The located assembly's manifest definition does not match the assembly reference. (0x80131040)
File name: 'System.Runtime, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'

I have tried changing the target (~/projects/AvalonStudio/AvalonStudio/AvalonStudio/AvalonStudio.csproj) to .NET 6:

<TargetFrameworks>net6.0</TargetFrameworks>

But this produced the exact same error.

I also tried:

~/projects/AvalonStudio/AvalonStudio/AvalonStudio$ dotnet run -f net5.0

But that also produced the exact same error. Any ideas what I might have done wrong?