It fails totally with our old app, but seems to work OK with 4.0; however, HWR/OCR/TTS are currently only barely working (very iffy) and we haven't yet decided whether to try to ship with those or to simply leave them out and consider adding them later if there's sufficient demand.
For HWR, our time would probably be better spent on allowing you to use a mobile device with a touchscreen as your input method, for OCR, since this would only be still OCR we don't necessarily need something as performant as our current system - and Apple are working on a built-in system OCR engine anyway, it just doesn't support Chinese yet - and for TTS, people can probably make do with the built-in macOS ones.
Also, a lot of our custom UI looks really, really bad on Mac, so we're tentatively planning to chuck that both on iOS and on macOS in 4.0. This will probably upset a few people if we take it to its extreme - for example, I'd really like to get rid of our built-in color picker, because iOS 13 and macOS 10.15 have a lovely new system color theme system where you can pick 'red' and then it will automatically adjust the shade of red based on day/night mode, accessibility settings, etc - but since we're planning to offer a "Pleco Legacy" app anyway, people for whom custom colors are more important than new features can simply keep using that one.