I am using VS2019. I have created a new WPF application for .net5. I copied 'readme.txt' to the project folder. I changed the output property of this file to 'Copy always'. In ClickOnce publish I go to settings / application files. I select 'show all files'. I change the publish status from exclude to include for readme.txt (download group: required, hash: include).
During publish I got a message 'Unable to apply publish properties for item readme.txt.'
I install the program to a client an the readme.txt is not there. Any idea? (This worked perfectly in .net4.8)
I have found the answer here. For the file in question you have to set "Build Action" to "Content".