Setting useMaterial3 applies certain defaults when constructed from the factory constructor, but since many themes are constructed from a default and customized with copyWith, they won't have correct typography or ripple effects. The code snippet below illustrates the missing defaults:

Copying my initial comment from a PR:

I would expect copyWith with useMaterial3 true to apply these updates, if I haven't provided my own typography and splashFactory, of course. If I understand correctly, we're currently requiring every created theme out there (that doesn't use the factory constructor) to add the following?

...
typography: Typography.material2021(platform: platform),
splashFactory: platform == TargetPlatform.android && !kIsWeb ? InkSparkle.splashFactory ?  InkRipple.splashFactory,
)

It's not documented anywhere and is pretty brittle.

Originally posted by @guidezpl in #104815 (comment)