It is possible to upgrade directly 9.7 to 11.1 via an offline backup
It is no longer possible to do this with 11.5. The error is:
SQL2514N The RESTORE was not successful. The backup used to restore the database contained a database with a release number that is not compatible with the installed version of the database manager.
We now need to do it in 2 steps via an intermediate version in-between.
9.7 -> 11.1 -> 11.5 works, for example
Since there are no transaction log changes between 11.1 and 11.5, I don't know of a reason other than maybe to save some development/testing costs. Can someone provide insight on why we do have this restriction at all?