Very interesting, thanks for posting. I had completely missed this as part of iOS 13. It's very cool they have implemented this, but I wish they also had a manual mode where I could set the maximum charge and change it on demand. 95% of the time charging to a maximum of 80% is the preferred behavior for me. But when I am going to be traveling, I typically want to top up to 100% so I can have maximum battery life. The phone will have no idea whether or not a particular day is a day where I want 100% charge or 80%. I suppose I could turn the feature off on those days, but its not entirely clear what that will do (will it lose all its previous learnings when I turn it back on?).
It's really the same use case as my car, I just wish they buried a user-configurable option somewhere in the settings.