Asp.Net Core 3.1 App sets the wrong runtimeOptions - .net-core-3.1

Question

I am developing a quick ASP.Net Core 3.1 app, and trying to push it to a Free Linux-hosted WebApp in Azure.
The app builds, runs locally, and deploys to a docker environment in Windows Azure. All the files are deployed as expected.
The challenge is this:
Upon starting the app using the command
dotnet <mywebproject>.dll
The log tells me this:
The framework 'Microsoft.WindowsDesktop.App', version '3.1.0' was not found.
First thing to check was to see if there was a missing runtime
root#4182491:~/site/wwwroot# dotnet --list-runtimes
Microsoft.AspNetCore.App 3.1.0 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 3.1.0 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
After some fondling, I see that there is a file named .runtimeconfig.json:
{
"runtimeOptions": {
"tfm": "netcoreapp3.1",
"frameworks": [
{
"name": "Microsoft.WindowsDesktop.App",
"version": "3.1.0"
},
{
"name": "Microsoft.AspNetCore.App",
"version": "3.1.0"
}
],
"configProperties": {
"System.GC.Server": true
}
}
}
So the runtime I need is there, but dotnet does not want to select it!
From the error, I am assuming that dotnet is attempting to start the website using the first framework that it can see, however how do I get rid of it during build? I've looked up how these files get generated during build, and can see no options to prevent a framework from being put into the runtimeOptions file.
Since I am building the app using Azure DevOps, I can't simply edit the file manually and upload it to the hosted linux container that it runs in.
So I need help with either:
How to build the project and EXCLUDE "Microsoft.WindowsDesktop.App" from the list of frameworks being generated
How to START the application in the linux container with a specific target framework NAME (I can only choose version from the settings I see in dotnet exec using SSL to the container.
This is more or less driving me nuts!

Answer 1

I am going to answer this one myself, since I found the solution after way too much coffee:
Turns out that the options you see here:
{
"runtimeOptions": {
"tfm": "netcoreapp3.1",
"frameworks": [
{
"name": "Microsoft.WindowsDesktop.App",
"version": "3.1.0"
},
{
"name": "Microsoft.AspNetCore.App",
"version": "3.1.0"
}
],
"configProperties": {
"System.GC.Server": true
}
}
}
Aren't options at all, but requirements. I found a dependency on a package designed for WPF that of course requires the Microsoft.WindowsDesktop.App runtime to be installed. Since I'm developing on a windows computer, the code had all the necessary runtimes to run in debug, but not on linux.
I'll close this for now, but since the naming led to confusion, I will leave the question up in case someone else runs into the same confusion that I did.