Thanks for your previous reply, and I wish you a happy new year, too!
Just to let you know that I could install rClr. The message "inferring 'repos = NULL' from the file name" can indeed be ignored as you said.
There was also an error message after running testthat. This can also be ignored.
So far everything I tried such as loading assemblies, creating objects, calling methods worked as described in the help file. Very good!