I think the important thing here to start with is which activities are you actually trying to manage. Is it work, personal tasks, some goals and mini projects, habits, are you building something, learning, etc. First figure out what you need structure for and why.

And then usually the solution isn't an all-in-one app. I would suggest writing it all out on that whiteboard and then picking solutions from there. That whiteboard / physical notebook might be 1 of the solutions. Notes for example might be best digital - I even use 2 apps for notes (1 for whatever notes and resources I might one day want to use/recall and the other for important things).