Can I leave Australia and travel while holding a subclass 491 visa?

The 491 is a multiple-entry visa for its validity period, so you can travel overseas and return while it remains in force. There is no rule that confines you to Australia.

However, the regional condition still governs where you live and work when you are in the country, and time spent overseas does not help you build the residence and income record needed for the subclass 191. Long absences can therefore slow your pathway to permanent residence even though they do not breach the travel facility itself.