Sleep not tracked

Could you post the screenshots of the following screens?

1. Health Stats » Sleep
2. Health Stats » Sleep with the Movement option enabled (see the button at the botoom of the grpah)
3. Health Stats » Heart Rate » current day
4. Health Stats » Heart Rate » previous day
5. Health Stats » Stress » current day
6. Health Stats » Stress » previous day

That could perhaps help seeing why the sleep detection does not work for you, though it works for others. Some possible reasons are bad fit of the wrist band, pacemaker, peripheral vasonstriction induced due to sleep apnoea, defectuous device, etc...

When there is no HR data, no Stress data, then there cannot be any Sleep data, of course, too. Does your watch show the HR? If not, check whether the HRM is enabled. If if is, then check whether your watch syncs to the app - when you sync the circle around the watch symbol at the top of the app must close and turn green. If it does, then it means you have your device associated with multiple accounts. Follow carefully and precisely all the instructions from the support document Data is Missing from My Garmin Account After Syncing to resolve the issue, even if you are not aware of creating multiple accounts (nobody is).