Activity cannot be converted to LifecycleOwner

You don't need to use

mLifecycleRegistry = new LifecycleRegistry(this);
mLifecycleRegistry.markState(Lifecycle.State.CREATED);

Since, new AppcompatActivity is already lifecyclerOwner.

You also observe class object, which is incorrect. actMain.class is a class object. You should have:

alarmViewModel.getAlarmList().observe(this, new Observer<List<Alarm>>() {
     @Override
     public void onChanged(@Nullable List<Alarm> alarms) {}
});