I created a .NET Core 3.1 AnyCpu Console Application using Visual Studio 2019 with the latest patches. The only code it contains is the boilerplate Console.WriteLine("Hello World!") it was created with. I compile this and it runs fine on my Windows 10 x64 box.
I copy the Debug folder over to my 32-bit Windows 7 box and attempt to run the Console Application. I get the following message. (The .Net Core 3.1 runtime is installed on the Windows 7 box).
The version of this file is not compatible with the version of Windows you're running. Check your computer's system information to see whether you need an x86 (32-bit) or x64 (64-bit) version of the program, and then contact the software publisher.
However, if I compile the Console Application using x86 then it runs fine on the Windows 7 box. With VS2019 and .NET Core 3/3.1 has AnyCpu changed? I would have expected that code compiled for AnyCpu should have worked fine under 32- and 64-bit.
It looks like there has been a change in the way AnyCpu works in .Net Core 3. In .NET Framework the .exe was a managed exe so with AnyCpu it JIT'ed at runtime to whatever was required x86 or x64 **. In .Net Core using AnyCpu the .Exe is a plain unmanaged exe, compiled for x86 / x64 depending on what architecture your machine doing the compiling is. However, the dll that it creates contains managed code and can be run on a 32bit machine using DotNet.exe.
The solution is not to compile on a 32bit machine as this just launches the dll in 32bit mode. The solution is actually to not use the .exe and launch the dll with the local copy of DotNet.exe.
** source: https://mihai-albert.com/2020/03/08/startup-sequence-of-a-dotnet-core-app/