It is perfectly plausible to conceive of a multitude of Universes (multiverse), each with their own characteristics and composition. There is no theoretical reason why our Universe should be the only one.
However, we have yet to find any hint of another Universe.
We are far from mapping our known Universe and its size is bigger than what we can actually observe. So who knows what lies beyond what we already know.
We happen to be in a Universe which sustains life but there could be other Universes where the laws of physics operating in them are vastly different from the ones in our Universe so that inconceivably bizarre things happen and weird beings prevail. We just cannot know.
Perhaps one of the big questions which will never be answered is this: How many Universes are there?