It does have the built-in python interface, but I think that has a pretty limited use case. You can gain access to all the java functions and libraries within openLCA (I think) and do some python-type stuff. But the python stuff is limited. I believe python is limited 2.X, and so I imagine a lot of modern libraries won't work well with it. I'm also not sure where you could place those dependencies to even have openLCA python find it.
Using the olca-ipc on the other hand allows you to use any version of python and whatever other packages you may want. The tradeoff is that you're limited to the functionality within the ipc, but you're still able to do A LOT, including making processes with inventories and product systems...all the stuff I think you're looking to do. It will just take some time to work through the IPC syntax to do it all.