Hello @SKV ,
sometimes there is nothing in any reference catalog available, but LeanIX is flexible, so in this case it does not matter, if you create you own. Self created business capabilities can be linked anytime to one of a reference model.
Application is (usually) a software used in a concrete use case by a user to execute a process. It is always assembled form one or more components. Often a Saas, software component are mixed up (by ICT, too).
E.g. you are using excel for reporting your expenses with ExpensesTemplate.xltx or xltm template. the software component is Excel, the application is ExpensesTemplate. Or you have a SharePoint based intranet, then intranet is the application and SharePoint is the software component. A system is a technical platform, the advantage for SAP users is the automatic creation with base information when you are using SAP discovery. I the past we did it manually by using the platform factsheet. Our success manager told me the system is a technical platform (assembly of subsystems, components and applications) and the old platform factsheet is now used for creating business platforms.
I hope this helps,
best regards,
Carsten