Large fonts

Both Android and iOS contain system settings to configure the desired font
sizes used by apps. Flutter text widgets respect this OS setting when
determining font sizes.

Font sizes are calculated automatically by Flutter based on the OS setting.
However, as a developer you should make sure your layout has enough room to
render all its contents when the font sizes are increased.
For example, you can test all parts of your app on a small-screen
device configured to use the largest font setting.

Example

The following two screenshots show the standard Flutter app
template rendered with the default iOS font setting,
and with the largest font setting selected in iOS accessibility settings.

Screen readers

For mobile, screen readers (TalkBack, VoiceOver) enable visually
impaired users to get spoken feedback about the contents of the screen 
and interact with the UI via gestures on mobile and keyboard shortcuts on desktop. 
Turn on VoiceOver or TalkBack on your mobile device and navigate around your app.