Upon upgrading Excel-DNA from 1.6.0 to 1.8.0 in a multi-project C# solution, I started getting build errors, and it seems to be because Excel-DNA is now autocreating launchsettings.json files in all Excel-DNA-enabled projects, not just the top-level (i.e. launch) project. It ignores the Visual Studio flag:
<NoDefaultLaunchSettingsFile>true</NoDefaultLaunchSettingsFile>
I should only have a launchsettings.json file for the top project (that actually gets built as an XLL for Excel) and the other 'helper' projects should never have any launch settings, as they are never registered as add-ins.
You should only see the launchsettings.json generated for projects that include the ExcelDna.AddIn package.
Library projects in your solution that are not to be published as add-in, should not include a reference to the ExcelDna.AddIn package. If they need access to the Excel-DNA types (like ExcelFunctionAttribute) you can add the ExcelDna.Integration package to these library projects.