When extending any of the models and declaring a property, I'm getting a TS error: Scheduler/Appointment.ts: TypeScript 'declare' fields must first be transformed by @babel/plugin-transform-typescript.
If you have already enabled that plugin (or '@babel/preset-typescript'), make sure that it runs before any plugin related to additional class features:
Thanks for sharing the tsconfig file but it's really hard to say what's wrong without debugging the issue. Could you please share a runnable test app with us so we can reproduce it locally and debug the issue for you? A runnable test case will make the assistance much faster.