Sorry about the delay, it is now available! You should be able to see "Ascend" button if you already defeated Extreme Zeus. Similar to how playstyle changed a lot on first layer to post-rebirth layer, the next Ascension layer playstyle is also quite different. Not sure how you'd fine it compare to previous 2 layer, so if you could let me know it'll be very appreciated.
and thanks for letting me know about the bug, it's now fixed!