Todo list: Nextcloud Deck, it has a web app and android app. Tasks here are usually long term, and I only update them infrequently
For quick notes and tasks Nextcloud tasks, on mobile I edit with opentasks, and sync with davx5, on desktop I edit them in Thunderbird.
Everything which has a date or deadline goes to the calendar. Again it’s nextcloud, synced with davx5, etar is my calendar app on android, Thunderbird on desktop.