

It’s called a looped timeline pair. Timeline 1 creates timeline 2, and timeline 2 creates timeline 1. Both timelines exist on an alternating basis. It’s one of the results of the bootstrap paradox. When people think of the bootstrap paradox, they usually think of single looped timelines. Those appear in media all the time. Harry Potter, Gargoyles, etc. But an unstable set of timelines can also stabilise across two, three, or more timelines instead of just one.
Out of the infinite versions of you in the multiverse, half win the lottery and half don’t. Which one your consciousness inhabits is pure luck.
Well, “no objective reality” is a lot more accurate to the truth of the world than any alternative. It might not be as narratively satisfying as a story where objective truths exist, but I suspect the human desire for objective truth is a cultural value that would be in our best interest to shed.