As other people say, something like 10% more effort to reach 2 platforms rather than a single one.
But _also_ (and that's no small deal), these cross platform framework often benefit from a huge skill transferability from web development, eg React Native or Vue Native. This is a massive deal, it means you can get a web dev to be productive on a mobile app pretty much immediately (and potentially you use the same technology as for your web app, which itself is also a big deal)
But _also_ (and that's no small deal), these cross platform framework often benefit from a huge skill transferability from web development, eg React Native or Vue Native. This is a massive deal, it means you can get a web dev to be productive on a mobile app pretty much immediately (and potentially you use the same technology as for your web app, which itself is also a big deal)