PB 2017 is the first appeon product. My understanding is that all versions prior to 2017, including your 11.x version, are SAP products and thus you would need to talk to SAP about any support they might be willing to provide. Having said that, I am fairly certain that sap will not provide any support for anything other than maybe 12.6 and even then i doubt you can get anywhere.
If you need to do anything to your legacy app, then you will eventually be stuck and unable to work on it. Just getting PB 11.x installed and running could be a problem. The old licencing they used may prevent you from installing PB 11.x on a new machine.
IMO, if the app has any value, then you should upgrade to a current version of PB (2019R2, or at least 2017R3)