I’m just using a self hosted git repo with markdown files. I was having trouble finding something open source that I could edit with vim that also had a good mobile solution. I also didn’t want to get locked into a file format that was specific to an app.
Markdown is ubiquitous and I use git all the time as a developer so it was easier to tack something onto an existing workflow. It’s a little janky but at least I won’t be screwed by devs abandoning whatever app I was using.
If you’re a terminal weirdo like me I’d recommend Taskwarrior