This is really well done, any plans for iOS?
This app is based on the source code from Astrid Tasks, which was licensed under the GPLv3. I'm under the impression that one cannot distribute GPL apps in the App Store, and I assume I would be legally required to license an iOS rewrite as GPLv3 since I'm intimately familiar with the original Android implementation.
That meme is rooted in an analysis and statement that the FSF made about the App Store agreement several years ago. Those terms have changed many, many times since then, but the FSF has never revisited the question of compatibility. The best thing to do would be to either read the terms to make a decision for yourself if you're confident that you can grok them, or to seek advice from a lawyer if not. But don't assume there's anything solid that can be concluded from dead memes.
Cool, maybe I'll have to buy an iPhone
Technically the Apple Reminders app can still be used with third party CalDAV servers, and third party clients can still synchronize with iCloud, but icloud.com, icloud.com list sharing, and Apple Reminders with your Apple account on iOS 13/macOS 10.15 now use a proprietary protocol.