It doesnt have to replicate. Thats optional. Can work 100% offline.
The RX here means it is reactive - i.e. you can subscribe to state and react to it. This is how it updates the display across independent tabs when the data changes, for example.
THATS the main point of RxDB, the sync is just another feature (which you dont have to use and isnt even a default).
EDIT: Im nothing to do with RxDB, and dont use it - but i have investigated it previously.
The RX here means it is reactive - i.e. you can subscribe to state and react to it. This is how it updates the display across independent tabs when the data changes, for example.
THATS the main point of RxDB, the sync is just another feature (which you dont have to use and isnt even a default).
EDIT: Im nothing to do with RxDB, and dont use it - but i have investigated it previously.