Still 20!
Someone in another thread mentioned their delve moving up to 160 from level 20, so mine being 20 is probably not big news. I only raised to 30 in the event. And I’m not sure you can even get away with that unless you do some unknown important steps exactly as I did.
I played one Crypt daily delve at 20 today and after that, my delve choices are still blank, 20 at x1, 30 at x2.
EDIT:
20 is the expected result if I were paying more attention. Explained here by Mithran: Delves: Strategies, tactics and tips - #449 by Mithran