emacs orgmode (+ mobile app) is incredibly powerful if you want something local and extensible.

The capabilities are insane, it can do TODO’s, scheduling, time-tracking, filtered agendas y lots more.

I have it synced with my iphone (the app i use is “beorg”, but on android a popular one is “orgzly”) and it kinda blows my mind

Barrier of entry for emacs is a bit high sadly