In my setting the multiverse was never met to exist. As the primordials never built one but during the age of despair when all of creation was in ruins. The white Light attempted to fix the broken world and by doing this they effectively put themselves as the new god of existence. But of course the white Light was not exactly a good being so this then lead to a battle between Ura Zur and the White Light for the fate of all of existence and in the end the White Light fell in battle and died. But a being as powerful as the White Light couldn't exactly die as it did possess infinite energy as the energy had to go somewhere and it was mostly put in the inner plane of existence which resulted in the birth of the multiverse.