Steps to Reproduce

Building a MacOS desktop app with default ThemeData (unchanged TargetPlatform) and running it on MacOS 10.12 seems to produce font problems.

Unfortunately I don't have a chance to test on MacOS 10.12, but a user report a weird font problem:

I have then tried to use Google Fonts to load alternative fonts, and this solved the issue. So it's definitely a problem with the default font of the theme.

Not sure if this is something which has to be fixed in flutter, since desktop is still just a preview and not sure if MacOS 10.12 should be "supported"(?). But I don't quite understand the problem, as the default theme on TargetPlatform.macOS uses SF UI and afaik this should be available since 10.11.