How can you track time spent on every app in the background?

Hey guys,

I want to be able to track my time spent in all apps in the background. For example I want to be able to track time spent on (Google chrome), (Slack), (Sketch), etc. I'm thinking something like this would be a native library written in Swift to run in the background. It would be great if its feasible with a React native library so it can be used for a mobile app to track app usage in iphone/android or use the experimental React desktop since I'm learning react and I think it would be a great side project to learn. Any input is great. I've looked around and noticed iOS already has a Screen time in the settings so using that library would be great. Any input would be great! Thanks