Did it ever work?

[LearningProcesss]

Hosted Dockerfile it's wrong

COPY ["Server/BlazorHosted.Server.csproj", "Server/"]

should be

COPY ["BlazorHosted.Server.csproj", "Server/"]

besides of that i don't think that can works if you don't provides Client and Shared project also

 ---> a225b4943a11
Step 11/17 : RUN dotnet build "BlazorHosted.Server.csproj" -c Release -o /app/build
 ---> Running in dff65dd5a60c
Microsoft (R) Build Engine version 16.7.3+2f374e28e for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  Skipping project "/src/Client/BlazorHosted.Client.csproj" because it was not found.
  Skipping project "/src/Shared/BlazorHosted.Shared.csproj" because it was not found.
  Skipping project "/src/Client/BlazorHosted.Client.csproj" because it was not found.
  Skipping project "/src/Shared/BlazorHosted.Shared.csproj" because it was not found.
  All projects are up-to-date for restore.
/usr/share/dotnet/sdk/3.1.426/Microsoft.Common.CurrentVersion.targets(1850,5): warning : The referenced project '../Client/BlazorHosted.Client.csproj' does not exist. [/src/Server/BlazorHosted.Server.csproj]
/usr/share/dotnet/sdk/3.1.426/Microsoft.Common.CurrentVersion.targets(1850,5): warning : The referenced project '../Shared/BlazorHosted.Shared.csproj' does not exist. [/src/Server/BlazorHosted.Server.csproj]
CSC : error CS5001: Program does not contain a static 'Main' method suitable for an entry point [/src/Server/BlazorHosted.Server.csproj]

Build FAILED.

/usr/share/dotnet/sdk/3.1.426/Microsoft.Common.CurrentVersion.targets(1850,5): warning : The referenced project '../Client/BlazorHosted.Client.csproj' does not exist. [/src/Server/BlazorHosted.Server.csproj]
/usr/share/dotnet/sdk/3.1.426/Microsoft.Common.CurrentVersion.targets(1850,5): warning : The referenced project '../Shared/BlazorHosted.Shared.csproj' does not exist. [/src/Server/BlazorHosted.Server.csproj]
CSC : error CS5001: Program does not contain a static 'Main' method suitable for an entry point [/src/Server/BlazorHosted.Server.csproj]
    2 Warning(s)
    1 Error(s)

Time Elapsed 00:00:01.39
The command '/bin/sh -c dotnet build "BlazorHosted.Server.csproj" -c Release -o /app/build' returned a non-zero code: 1

Am i wrong?