MS to-do is my go-to. Multi platform and has all the features I need. Open source Linux option is “AO” on GitHub.

https://github.com/klaussinani/ao

Not op. I've been using "habits" for recurring things

Do you mean Loop Habit Tracker? Once it's installed it shows up as 'Habits'.

I did. I didn't realize it went by two names

Use org-mode or die.

..if you live long enough to set it up.

But do you keep your todos for obtaining the necessities of life in one agenda file or split them up by theme ...

I use TickTick, and it’s daily task seems to work well for me. I have a “morning check” and a “night check”, each with some sub-tasks.

Todoist - https://todoist.com