Is NoSQL vertically not scalable?
NoSQL is horizontally scalable because it supports hierarchical structures, which means that at any point in time, you could further establish a relationship with any data, such as parent: child.
Does this mean similar scalability is not possible horizontally? No, An example is MongoDB can scale vertically by adding more resources to existing machines.
It's always preferred to scale horizontally because its cost-efficient, processing power stability, hardware-efficient, and less downtime while migration :)