I have an iOS Flutter and a webapp that talks to this as a backend for my business. It is private and all low usage, but I like the idea that this is infinitely scalable and doesn't require any effort to maintain.

Infinitely scalable's a bit of myth in my experience. We've switched firebase app to a small postgres instance and have seen all of our performance issues magically melt away.

Firebase is a service that encompasses a bunch of things.

Do you mean Cloud Firestore?

To be clear, when I reference the infinite scalability, I mean the ability of cloud functions to spin up as many instances as I need.

In terms of database load, I'd fully expect to have to migrate to a larger instance, but that is also relatively easy with cloud sql postgres.

Cloud Firestore how does that relate to Datastore? Really wish Google would allow multi-region Cloud SQL like AWS allows with RDS. Datastore is such a pain to use with its index requirements

Firestore is the next generation: https://cloud.google.com/datastore/docs/firestore-or-datasto...

Ah yeah, I was mostly talking about the database offerings. The cloud functions can scale infinitely.

Cloud Firestore scales just fine, like any database, you have to know how to work with it. You switched from a nosql database to a sql database... two totally different performance profiles.