Sometimes Fortnite shows an error when downloading the launcher in a Mac OS and at that time click on it with the right click button and then delete the 'pkg.info' (if it is there) in the "Show package content"! Then shut the whole launcher and then restart the launcher and you would see it working!

I already bought an iMac and that is the only device I have at this moment! But I also suggest people downloading Windows software via Bootcamp and that helps me use Windows software and the apps that only run in Windows!