If you’re looking for an explanation of the universe, which is a collection of contingent beings, there are only two possibilities: 1) The explanation is found in a necessary being that transcends the universe; 2) There is no explanation.
Regarding 1), every physical entity is a contingent being. The “universe” simply refers to the whole collection of physical, contingent beings. One cannot explain why the universe exists by appealing to another physical, contingent being because there can be no physical, contingent beings outside of the collection of all physical, contingent beings. “But,” one might say, “perhaps it could be explained by a prior non-physical, contingent being. Perhaps, but even if so, as a contingent being, that non-physical, contingent entity would also require an explanation for its existence. To avoid an infinite regress, one must ultimately arrive at a necessary being that transcends the universe, and explains why the universe exists.
If you reject 1), then you are left with 2). Is this rationally satisfying? Option 2) means one must reject the principle of sufficient reason, and think that some contingent beings just exist as a brute fact, without any reason for their existence. While this is outlandish enough for an eternal universe, it is preposterous for a universe that came into being. Surely something that comes into being must have a reason why it came into being. To reject 1) in favor of 2) is to abandon reason. There is no reason to opt for 2) apart from an a priori commitment to atheism. While 2) is consistent with atheism, it is not consistent with what we know about contingent beings. Contingent beings, by their very nature, do not have to exist, and at one time, did not exist. There must be a reason for why they exist, and a cause for their being.
Which option will you choose?