I got this figured out. I was importing @auth0/cordova like all of my other typescript imports:
import { Auth0Cordova } from '@auth0/cordova';
This didn’t properly import, so it was trying to call onRedirectUri on an undefined object. Changing it to below (same as the quickstart) fixed this for me. Just had to ditch the curly brackets.
import Auth0Cordova from '@auth0/cordova';