Filen checks off most of your requirements https://filen.io/
- Auto-sync between my Android phone and Linux desktop
- Journaling
- Quick notes
- To-do lists
- Planning
- Writing down thoughts
- A really good Andoid app
- Easy to use
- Free for personal use
Filen is missing project management stuff like Kanban etc, just use cryptpad for that. Cryptpad https://cryptpad.fr/
Edit: Another comment mentioned Plane, I’d recommend it over Cryptpad. Cryptpad is really barebones in comparison even though they’re growing and adding features and integrations.
My recommendation is now Filen + Plane https://plane.so/
Thank you, I just created an account with Plane, looks great!