pg_restore: [archiver] unsupported version (1.11) in file header postgresql
PostgreSQL really doesn't put much effort into supporting moves from newer major versions back to older ones.  One big reason for that is that newer versions usually support features which you just can't install on older versions; although any given database might not be using any of the new features, the project philosophy is that they would rather not support it than to support it in a buggy or incomplete fashion.

Your best bet might be to generate a "plain" format dump rather than a "custom" format dump.  This is just a text file of SQL commands.  If you aren't using any new features, it might just apply cleanly.  If not, you can look into the errors and decide what to do for a back-port.