Thanks. That helps explain things.
You're working within the Drives & Devices section of Media Center. This allows you to view files as they are on disk, but if you have it set to All Files mode, it shows files whether they've been imported or not. You're not having luck adding Genres because when you added the first one you were working on a file (or files) that had not been Imported into the Media Center Library. Neither is that other one you have selected in the screenshot, for what it's worth.
In order to see the files in all of the Views of Media Center, access the files in your Views, add them to Playlists, and generally use them within Media Center you need to Import your files first:
https://wiki.jriver.com/index.php/ImportThe Drives & Devices part of the tree, if set to
All Files Mode (as you have it in your screenshot) will let you see and work on all files on disk, even those that haven't been imported. However, any changes you make there on non-imported files won't impact the Media Center Library (database) and will only be saved to that file's tags itself (and then only if the file in question supports tagging). It won't change the drop-down options available elsewhere unless the files are Imported and in the Library. You won't even be able to
see those files anywhere else in Media Center (anywhere under Audio in the Tree, for example).
You can Import files right from within the Drives & Devices View you're working within, if you want, by selecting the files on the right and clicking the
Import into Library button. However, you'd probably be better off importing your entire set of media files in one fell swoop using Auto-Import:
https://wiki.jriver.com/index.php/Auto-Import