For To-Dos, I'm trying out KDE's Kalendar for my laptop and Tasks.org for my android, both synced using a Radicale server on my laptop.
For ordinary notes im just using Markdown files in a folder. Markor on Android and VScodium on desktop. Synced using SyncThing.
Its a hot clunky mess for both setups but it works for now I guess. I do want to build a gtk app focusing solely on To-Dos that incorporate all the features of my plugins but as i mentioned before, a huge problem is time availability