Where does SQL Server store symmetric keys? I am wondering if symmetric keys created in particular database are being stored in the primary file group?

Or they are stored in some special file group which the user is not able to interact with?

For example, if I am performing a partial backup to a file group (primary or secondary) can I be sure that the backup does not contain the symmetric keys?
The underlying system tables used by the sys.symmetric_keys catalog view are stored on the PRIMARY filegroup along with other database meta-data.