I am one of those who is never been satisfied with my
current calendar/todo/task/planner solution that's because we are productivity nerds. Every year or every few years you tend of optimize what you are doing as you get comfortable with your current solution because you want to add more to it as the number of things you want to track grows and expands.
Over the years my calendar has become something to remind & track my recurring tasks and events. I use a physical notebook as my planner(daily/weekly tasks) and note taking (almost like a bullet journal) but I also use Trello for project tasks and long term goal & its related tasks. I am not a fan of Notion but people love it so I have to use it when I need to collaborate with people.
And this is my current setup from past 18months, before that I relied heavily on my calendar for most tasks. But at some point it felt weird being stuck on the calendar and it ended up being a distraction as I was exposed to other things in my calendar most of the time. Your brain doesn't stop thinking about what you just read even if its not immediate.
The thing is, the more you dig deeper into optimizing this, the more holes you find in your system as everything at this point leads back to you(the user) actively needing to go to those systems yourselves.
Plus this product is for e-ink tablets, which is currently a niche product and as people switch to new products its easier to have a better optimized solution for it than going back to older solutions which requires weird ways to sync on the new device or something. I don't know how difficult working on other apps is on e-ink as I don't own one but generally moving away from heavy smartphone use over the years has taught me that these systems can work very differently on various platforms.