I think it's obvious that multi terabyte repos are not the norm.

How did they even manage to generate a terabyte sized repo, that's crazy. Do they have something written up on how it's structured and why they'd even go that route?

It couldn’t be broken in to domain specific components?

Listen, I am a rails developer, so a monolith doesn’t scare me, and yet, there are limits. Why does it need to be a multi terabyte monolith?