I agree for dynamic typed language like python and javascript 10-20k is a good limit. With a static typed language like C++, if the abstraction is well designed people should be able to handle more.
The project I'm working in atm is neatly structured and at ±60K, but you definitely see certain team members knowing more about one part than the other. We've also started a POC to start moving to Typescript for the more critical areas of the application (services, data models).