How is Blink Shell: Mosh & SSH Client[1] licensed as GPLv3 on the iOS App Store? To my knowledge that's not the only GPLv3 app on the iOS app store. Many of the projects give a special grant for it to be published on to the app store.[2]
I’m not even sure a grant is necessary. As the author, you can relicense your work whenever you want. That includes relicensing for a certain platform. So, release your GPLv3 source code, but release the “proprietary” version on the App Store.
If you're the sole author yes. If you took any contributions then no unless you got all the contributors to accept your proprietary license for their contribution.
Actually clicking on the "License Agreement" link pops up a copy of the GPLv3 License, so it looks like you can distribute GPLv3 software in the app store (and charge for it!)