Figured out the below answer in the Firebase repo fixes the issue:

I've discovered if I move the db = firestore.client() into my cloud function, I'm able to deploy.

https://github.com/firebase/firebase-functions-python/issues/126#issuecomment-1682542027

It's really weird that Google does not update the docs or fixes the issue, but for now, this answer unblocks me, hope it helps others too.