But beyond that unmanifested is another unmanifested being, eternal, who does not perish when all beings perish.

Crucial distinction: paraḥ tasmāt — beyond that (the causal avyakta of 8.18) there is anyaḥ bhāvaḥ — another state of being. This is the avyakta sanātana — eternal unmanifested.

Na vinaśyati — is not destroyed — sarveṣu bhūteṣu naśyatsu — even though all beings are destroyed. This is the absolute Brahman, not the causal state of the universe.