I'm using an .md file that I sync with Nextcloud between all of my devices. I edit it with Obsidian on my laptops, and the Nextcloud Notes app on Android, which

I'm using an .md file that I sync with Nextcloud between all of my devices. I edit it with Obsidian on my laptops, and the Nextcloud Notes app on Android, which also has a nice widget that allows me to pin my todo.md on my homescreen and formats the markdown checklist appropriately. It's the most flexible system I've ever used. The only missing features for me are the ability to reorder items quickly on mobile and add reminders to a todo. But control over my own data beats both of those features.