I published a set of open source control strip widgets that use event-driven services as models here: https://community.folivora.ai/t/a-standard-set-of-responsive-energy-efficient-widgets-volume-brightness-calendar-timer-world-clock-git/3083/
My project separates things into a MVC pattern for easier testing and configuration. However, if you want to combine models and controllers, another person wrote a simple timer that pushes appearance updates directly from a service: GitHub - iOliverNguyen/tomato: Tomato is a command for running pomodoro in background. It's designed mainly to stay in MacBook touchbar.
It’ll be to this community forum, but I can link to it in this thread once it’s ready.