104days is a free iOS app. It has no monetization strategy. It's an app I wrote for myself, a gift to my friends and, by extension, the wider world.
104days doesn't want your data. It doesn't collect your data. All your data stays on your device. There are no server-side components.
In January 2018, I took the decision to remove all tracking code. Prior to this I was using Google Analytics to work out how people used the app and for my own amusement. It gave me no useful information.
If you opt-in to Apple's Share analytics, diagnostics, and usage information with Apple feature and choose to "Share With App Developers" then I have access to anonymous usage stats and crash reports. I use these to stoke my ego and to help make the app better.