the problem with iOS was that you had to pay 99$ a year to upload apps to your own phone, which prevent use of GPL code since it removes your right to do stuff on your own hardware. Fortunately this restriction was lifted since Xcode 7 a few years ago and it's nowadays not a problem at all - there are plenty of GPL / LGPL apps on the app store. Just put the code and build instructions on github, what matters is that users can patch, rebuild and upload the patched version to their phone.