I found a nice way to handle my private todo tasks and share them between my computers and phone:

• Radicale (CalDav server, implements todo)
• Errands (libadvaita app for GNOME, syncs with CalDav)
• Tasks.org (installed via F-Droid without subscription, app for Android)

It's pretty neat, works with subtasks, colors, tags, and my family and private calendar.