Yeah, it's two separate monorepos. There is actually some shared code between multiple monorepos. Code like IDL's and some C mapping code are shared, but they are referenced as vendor libraries so each monorepo updates those dependencies when they need to. If you think about Android vs iOS vs a web based dispatch system vs an autonomy system; They are all totally different. All of the code, dependencies, vendor code (external dependencies), and tools in each monorepo are "platform" specific and live in each respective monorepo.
Each monorepo is solving one cognitive problem domain with all of the libraries and dependencies that go with it usually for a target platform. Every iOS app that Uber builds lives in one repository — you clone that down and you can build Rider, Driver, Eats, Freight, and Jump. They all use the same networking stack, same UI stack, same map stack, same VIPER architecture, etc. This makes it easy for someone who is an iOS dev to work in any app or spin up a new app with almost no effort.
But, you're right... it's not a monorepo in the sense that all of the code in the company is in one place. Maybe I like micro-monorepos.