I don't understand why this app was so difficult? How complex is it? Doesn't all it do is detect when another phone is nearby and send the data back somewhere? I heard it's draining on power, because blue tooth has to be on all the time. [...]
And another wrinkle with the Android version of the Apple/Google "exposure API" - it's being distributed in an update to the increasingly-misnamed "Google Play Services". This means that it probably won't work any time soon on Android Open Source Project phones, which includes freaks like me using LineageOS but also the "blocked" Chinese manufacturers like Huawei, Xiaomi, BBK (better known here as OnePlus), TCL (Alcatel), ZTE, Tinno (Sugar), and so on.
Obviously, cutting off large parts of the Android phone market is another problem when you need a critical mass (some say over 20% of the population, others over 60%) to use the app for it to be effective even if it they get it working correctly.
The German app uses the exposure API. I've not checked whether D3PT is different.