I've got this problem: "Published .Net Core App Warns to Install .Net Core but it's Already Installed"
I searched on Stack Overflow and found the answer:
In my case I had the same issue, and the problem was that I was not deploying the file "MY_PROGRAM_NAME.runtimeconfig.json". After copying this file, which is present in the build output, the application launches without any problem.
I don't know how to deploy this file, and I have to deploy the file .runtimeconfig.json in the app I use or in .Net Core 3.1 Runtime.