If your codebase can’t fit on a single developer dev machine it’s too big.
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?
Even with a git history, wouldn't that only be maybe a few hundred MB?
People usually mention git-lfs at this point, but that is always annoying to use in practice. There is also shallow-clones and sparse-checkouts, but these only mitigate the problem as there is no way around cloning at least one revision completely with git.
Obviously a 20 year git repo with all commits is going to be massive, but you don't need that locally.
Also, it seems like it would be reasonable for a AAA game to version control assets separately from code.