Difference between new Observable(...) and Rx.Observable.create(...)?

There is no difference. Observable.create calls new Observable.

As the manual says,

Observables are created using Rx.Observable.create or a creation operator

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Rx.Observable.create is an alias for the Observable constructor

Observable.create is conventionally used, probably because it reads better in chains and conforms with other Observable static methods that create observables, too.

The difference may appear in child classes. For example, Subject.create is equal to AnonymousSubject.create and not equal to new Subject. Usually Subject.create is the one that provides desirable behavour, while new Subject is more low-level. This confirms the point about the convention.

On the other hand, some classes (notably BehaviorSubject) are supposed to be used with new because create signature doesn't allow to provide the desired behaviour to them.

The two are interchangeable, but the inline documentations says that Observable.create is deprecated (future proof link here).