Currently, it is possible to multi-target modules. This is neither a warning nor an error.

However, the guidelines state:

§2.6 Avoid targeting additional frameworks such as net7.0.

Why? Due to current limitations (1, 2) on how modules are loaded, Cake attempts to load all assemblies included in the NuGet package of the module (of all targets) which causes warnings to be displayed and the impression that the module was not loaded and/or is not working. Once those limitations are fixed, we'll update this recommendation to align with the recommendations for Cake Addins.