You can accomplish this with a monolith too though. The service part is doing no work. And a stateless monolith is even easier to scale than a database.

Monoliths certainly can reach their breaking point for other reasons. But they can take you very, very far too. Depending upon your exact use case, a stateless monolith, Postgresql, and something like Redis can handle millions of daily users.

It's been a while since I've had to do this, about 10 years. The breaking point for our use case was around 6 million daily users. I would imagine you can take it further today, but haven't had the need to so I don't really know.