How do I create a new genre?

I was able to read in a genre-tag from my iTunes metadata and convert it as a new genre, but I can I create a new genre in Roon from scratch?

You can’t create your own Genre ‘from scratch’, you may use Roon genres or Genres from file tags - these are the only available options. The workaround here is to add genre you want to have in Roon to the file tag.