Die Selected Altitude kommt über Mode-S Enhanced Surveillance (EHS), daher kein ADS-B notwendig dafür.

https://skybrary.aero/articles/mode-s

Siehe unter "Mode S EHS (Enhanced Surveillance):

Selected Altitude - the flight level which is manually entered in the FMS by the pilot. Selected Altitude provides an indication of the intended flight path and should reflect the ATC clearance with a few exceptions. It is used to improve controller situation awareness and conflict detection tools. The use of Selected Altitude values in Safety Net systems is expected to considerably reduce false alarms (an STCA study showed that by using Selected Altitude more than 90% of all false alarms could have been avoided) for aircraft engaged in vertical manoeuvres (level-off scenarios)and, thereby, to considerably increase the performance capability of the Safety Net systems. At the same time, the display of the Selected Altitude in the track label (either fully automated for cross checking with controller input or just presented as additional information) has proven to be an efficient tool to identify and mitigate the risk for potential level busts.

Wie das beim Lotsen aussieht hier:

https://skybrary.aero/articles/use-selected-altitude-atc

EDIT: Entweder hab ich die Beiträge oben übersehen oder das Forum spielt mit einen Streich und zickt. :-)