mmmmh I’m guessing it’s a warning not an error, if you are facing this msg
(getRootNav) is deprecated and will be removed in the next major release. Use getRootNavById instead.
if so, don’t know but personally I still use
this.app.getRootNav().setRoot(HomePage);
till I see the proper solution https://forum.ionicframework.com/t/getrootnav-deprecated-use-getrootnavbyid-whats-the-value-of-the-root-nav-id/