.NET Core 3.1 desktop application fails with error message, “This version of %1 is not compatible with the version of Windows you are running.”

My .NET Core 3.1 desktop application is working fine for a few hundred users. One user is having trouble. He is running 32-bit Windows 10 on a 64-bit CPU. I am guessing that might be significant because most users are running 64-bit Windows. I have confirmed via a screenshot that he really is using 32-bit Windows with a 64-bit CPU.

To use .NET Core 3.1 desktop apps, users must install the appropriate .NET Core runtime files. I send users to the following page:

https://dotnet.microsoft.com/download/dotnet-core/current/runtime

... and tell them to select either 32-bit or 64-bit under the "Run desktop apps" heading. The user has done that, and he downloaded "windowsdesktop-runtime-3.1.5-win-x86.exe" and ran it to install .NET Core 3.1. He said there were no errors or warning messages when running that installer.

Unfortunately, he gets an error message when he tries to run the app, "This version of %1 is not compatible with the version of Windows you are running."

It's evidently a bug that the message includes "%1". I assume that is an overlooked substitution placeholder.

I believe I am creating the app correctly. Here are the settings from the .csproj file:

WinExe
netcoreapp3.1
true
1.2.2.0
1.2.2.0

My platform target is "Any CPU", Prefer 32-bit is unchecked. The app is very simple, but does use WinForms. None of my code executes so I don't know what you'd need from my project, if anything. The only other lines in the .csproj file are a couple references to my source files.

Why is the user getting the error when he tries to run the app?

Is there some .NET install step he needs to do even though other users succeed in running the app?

What further information can he supply that will help diagnose this issue?