Elements.Playground doesn't run

[ivanachillee]

Describe the bug
Getting this when doing dotnet watch run inside of the Elements.Playground dir.

Unhandled exception. System.Text.Json.JsonException: '<' is an invalid start of a value. Path: $ | LineNumber: 0 | BytePositionInLine: 0.
 ---> System.Text.Json.JsonReaderException: '<' is an invalid start of a value. LineNumber: 0 | BytePositionInLine: 0.
   at System.Text.Json.ThrowHelper.ThrowJsonReaderException(Utf8JsonReader& json, ExceptionResource resource, Byte nextByte, ReadOnlySpan`1 bytes)
   at System.Text.Json.Utf8JsonReader.ConsumeValue(Byte marker)
   at System.Text.Json.Utf8JsonReader.ReadFirstToken(Byte first)
   at System.Text.Json.Utf8JsonReader.ReadSingleSegment()
   at System.Text.Json.Utf8JsonReader.Read()
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
   --- End of inner exception stack trace ---
   at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& state, JsonReaderException ex)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.ContinueDeserialize(ReadBufferState& bufferState, JsonReaderState& jsonReaderState, ReadStack& readStack)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.Deserialize(Stream utf8Json)
   at Microsoft.AspNetCore.Hosting.StaticWebAssets.StaticWebAssetsLoader.UseStaticWebAssetsCore(IWebHostEnvironment environment, Stream manifest)
   at Microsoft.AspNetCore.Hosting.StaticWebAssets.StaticWebAssetsLoader.UseStaticWebAssets(IWebHostEnvironment environment, IConfiguration configuration)
   at Microsoft.Extensions.Hosting.HostBuilder.InitializeAppConfiguration()
   at Microsoft.Extensions.Hosting.HostBuilder.Build()
   at Microsoft.AspNetCore.Components.WebAssembly.DevServer.Server.Program.BuildWebHost(String[] args)
   at Microsoft.AspNetCore.Components.Web.DevServer.Commands.ServeCommand.Execute()
   at Microsoft.Extensions.CommandLineUtils.CommandLineApplication.Execute(String[] args)
   at Microsoft.AspNetCore.Components.WebAssembly.DevServer.Program.Main(String[] args)

I've just cloned the repo, did dotnet build at the source, and then dotnet build inside Elements.Playground and getting this error when trying to run the playground.