What system type is the MacBook Pro 2013 operating system MacOS Catalina version 10.15.6 ?

macOS has a Unix-based kernel system. Catalina specifically is a 100% 64-bit architecture (which means it doesn't run old 32-bit apps anymore).

It is MacOS Caralina 10.15.6.

What does your question mean? What are you trying to find out?

You said you have MacOS Catalina version 10.15.6.