In its documentation, Apple seems to refer to these in vague words, as indicators. The bottom bar doesn't seem to have an official label. From Daring Fireball:
Apple seems to be going out of its way not to give the horizontal bar
at the bottom of the iPhone X user interface a name. For example, in
the “getting started” pamphlet that ships in the iPhone X box, they
don’t give it a name. They just show a picture of it, with an arrow
indicating the gesture, and say “Swipe up to go home.”
Those of us who write about these things need a name for it, though. I
suggest “home indicator”. In Apple’s Human Interface Guidelines for
iPhone X, they use a similar but more verbose construction: “the
indicator for accessing the Home screen”.
UPDATE: It’s also called the home “indicator” in the UIKit APIs.
(Thanks to Sachin Patel.)