I never had the need to scale an event store. I developed and supported in production a SQL Server based event store. I had benchmarks of 1000s tps on it but never came close to that in production.

What do you need to scale?

If you need to scale the writes you can model your streams to have many (millions) of them and keep them short. You can use sharding to scale horizontally the data.

If you need to scale queries you can put read-models in place.

If you need to scale event stream reads you can use sharding or put some caching in front of the event store stream reads.