Big fan of the work on your app as a fellow developer. It's my favorite to-do list application I've tried of many. I've bought both ioS and Mac version.
The biggest feature that is missing on MacOS and is Multi-Window Support. I need to be able to open multiple windows with different lists so that I can reposition them in different spaces on the screen as I'm often managing multiple tasks at once and prevents me from fully using the application how I'd want to.
Also another great usability feature is the quick task add dialog box. Using the hot key that opens this requires me to press escape to close. Instead other software I found, opens a dialog box with a toggle on/off of the hotkey. This may seem minor but adds significant friction throughout the day.