In addition to the other great responses here, I’ll add that the existence of closed systems has not been established. Cycles can occur in open systems, but there may be no end to the possible forms of cyclicity, not everything cycles.
Also, eternity may be a timeless phenomenon. Take for example the zero value of t at the speed of light. Relative to the reference frame of a photon, time doesn’t exist. Time is a subcomponent of spacetime. Can there be cycles where there is no time? Is there something beyond spacetime? It could itself be an emergent property of something timeless.
This topic is beyond the edge of our current scientific insight, but this only makes it more exciting lol