There's a really awesome GitHub repository that I like to check whenever I have questions like this. Conveniently, they happen to have a section on task management software. Check out https://github.com/awesome-selfhosted/awesome-selfhosted#tas...

Off topic: May I ask why you prefer open source and self hosting, other than obvious benefits like transparency, ability to patch your self, data ownership. There are obvious drawbacks too like project going unmaintained. Managing a server is not a drawback if there is only fewer users.

After trying several I keep going back just pages in notepad++, or Zim wiki

Interesting how after many years and hundreds of apps there is no todo killer app. There is still space for someone to come up with something truly effortless and practical, or maybe it just does not exist

Task Warrior

https://taskwarrior.org/