All the default apps are, and a good number of third parties, but a few appear is if they’re using a scaled up iPhone X/xs/11 pro UI, where everything is just ever so slightly bigger. I wasn’t sure if my eyes were deceiving me, but here are a few screenshots to compare the keyboard sizes:
Left: mail app, right: Monzo
It’s not a new screen size but the view port is new! It’s narrower than the 11, but also taller than the 11.
https://mobile.twitter.com/stroughtonsmith/status/1316113451547332608