I'm sometimes amazed by project sizes, a 30k line codebase is small? I'm aware that the ceiling is high but 30k lines of code can encode so much information and behavioural nuance.

Maybe this is just my backend/network focus with Golang though. Scaling beyond 10-15k lines of code always was quite intimidating as it is usually where I lose the ability to just keep a model of the codebase fully in my head.

Heavily depends on what you're building. A SaaS app with multiple front ends will easily hit 30k.