On .NET, Saxon 8.9 omitted the saxon8api.netmodule file. This file is needed when developing Saxon applications in an environment such as Visual Studio. Saxon 184.108.40.206 rectified this omission for Saxon-B, but in Saxon-SA, the file is still missing.
The same file is applicable to both environments, so you can use the Saxon-B version in Saxon-SA. For convenience, a copy of the file is attached to this bug entry. It should be installed in the bin directory containing the DLLs.