BUG: Managed CustomAction Nuget package will only install in .Net 7 but .Net 7 not compatible

[BryanCrotaz]

WixToolset.Dtf.CustomAction will only install from Nuget into a .Net 7 project and not into a Framework class library. But it says elsewhere (https://stackoverflow.com/questions/60752425/is-it-possible-to-create-a-wix-c-sharp-custom-action-project-for-dotnet-core-3-1) that you can't use .Net 7 custom actions. Please, some docs...

I've installed the Nuget package into a framework 2.0, 3.5 and 4.8 class library. It says it's installed, but it's not listed in the project Dependencies/Packages, and the compiler can't find the classes.

I'm trying to build an action that will simply download a file from the server with a licence key from the MSI UI passed in the url. That file needs to go into my install directory.

If there's an approved way to do this, maybe someone can point me at the docs? Or tell me how to build a managed custom action, or tell me how to build a JS custom action (that doesn't work either - it treats the js as a wxs file!)