I persoanlly find these answers usatisfying. They are simply semantic, of course if you define the universe as all there is then there is nothing else. But all that tells you about is your own dictionary.
There are many ways to define the word universe, one might mean the observable universe. i doubt anyone thinks that unvierse ends there. Others ,for example those favour the eternal inflation model, propose our universe is a bubble in a see of inflating space which contains other bubble universes. We might also consider temporal boundaries too. Was there a universe before ours? Many theories such as Loop quantum gravity suggest so.
But the truth is nobody knows the answer to these questions. The problem is there are two horizons that we can't see beyond. The first is our spaital horizon, the maximum distance we can see, limited by the speed of light and time since our our temporal horizon; light can't travel beyon the time the CMB was emitted about 400 thousand years after the big bang.
Now there is sime hope though, it may be possible to detect what happened - if anything - before the big bang via observing primoridal gravitational waves either directly from some (probably far) future gravity wave observatory such as the big bang observer or indirectly though how it imprints on the CMB. Also some have argued that if the eternal inflation picture is right we might see traces of it in the CMB too.
None of these observations have happened and they might never happen, so right now no one knows what lies beyond our horizons.