Access to real-time data of custom activities

[SunsetRunner]

I would like to create & log custom activities in FitBit. I know you are not keen on 3rd party apps retrieving detailed activities, but is it allowed for apps to only retrieve the activities logged by themselves? For example, I would like to create an app where it logs activities while working at a desk, then I want to show these activities as well (so need to be able to retrieve them again).

So the app does not need any access to other activities then the ones it creates itself.

[JonFitbit]

It sounds like you want to use the Exercise API to log custom exercise activities. https://dev.fitbit.com/blog/2018-12-17-its-time-to-exercise-with-fitbit-os-3/#exercise-api

You can retrieve them again using the Web API https://dev.fitbit.com/build/reference/web-api/activity/