On iOS:

The default Navigator.push() API produces an
iOS Show/Push style transition that animates from
end-to-start depending on the locale’s RTL setting.
The page behind the new route also parallax-slides
in the same direction as in iOS.

A separate bottom-up transition style exists when
pushing a page route where PageRoute.fullscreenDialog
is true. This represents iOS’s Present/Modal style
transition and is typically used on fullscreen modal pages.

Platform-specific transition details

On Android,
two page transition animation styles exist depending
on your OS version:

Pre API 28 uses a bottom-up animation that
slides up and fades in.

On API 28 and later, the bottom-up animation
slides and clip-reveals up.