Was looking for the same for ages. Every option I found was either some bloated docker solution or a dead project.
Gave up and just created a repo named “Todo” on my git server. It’s not really designed to be used for this kind of stuff but git and a web ui works perfectly fine. Just open a new issue. Give it a title and a brief description, a due date and some tags. Then you can create more subtasks, add comments to each, references etc. Even got my non-technical wife to use it.
With some customization you could probably get exactly what you want.
Edit: just realized you probably wanted something more simple. Set up a caldav server and sync the tasks using your preferred to-do app.