I myself am experimenting with a feature, available with Google calendar on mobile: Goals.
It is meant to help you hack your calendar, and apparently, it learns your habits.
You can set up a goal, say, "learn German", tell Google Calendar how often you would like to be doing it, when you prefer it to take place and for how long. Google Calendar then finds time slots and automatically schedules it for you, leaving you only with an option to "just do it" ✔️
It reminds you about the goals and then asks if you have completed them. You can defer on your goals, which should teach the Calendar to pick a better time. My experiment is currently ongoing.