Answer:
Yes, it is. There are no known surroundings in the universe.
Step-by-step explanation:
The universe is an isolated system because there are no evidence of the existence of surroundings in the universe, therefore it is a closed system and all the closed systems can be considered as isolated. There are some theories like multiverses or others but the have not been corroborated and thus, the universe is still benn an isolated system.