You chose to nitpick a possible implication of my comment with ”Are you saying…”. That’s silly. So let me actually say something about that point so we can have a conversation on stuff that I said, not about your imagination.

I believe it makes no sense to design an animation to uncheck a checkbox in a habit-tracking app. The only occasion when this will be used is when a user accidentally marks something as done (with a long-press, which makes it even more unlikely). It is definitely important to allow that. But there is no reason at all for that action to also have an animation. There is nothing to celebrate in that fixing action.

I think it would be even ok to hide that action of unchecking behind a “Edit”, so it doesn’t add noise by showing something that will not be considered to be used 99,9% of the times.

You can unmark the habit as completed, but you don't interact with "the big checkbox" to do that. Shortly after you interact with the satisfying checkbox described in the article, it disappears to show you a visual representation of a mountain that you're building and climbing by doing your habit. To mark a completed day as incomplete, you enter a different UI that has a calendar-style view, and tap on the completed day.