When creating (or updating) a User Story or an Enabler in a Team that is associated with a Program, the potential parents should be proposed in the parent selector (direct artifact creation and modal).
Trackers are subject to be covered: trackers that can be planned in the Team backlog (ie. User stories, Team Enablers)
Parents that are subject to be proposed: open artifacts from trackers that can be planned in a Program backlog (ie. Program & Program Enablers).
This means that a User Story could end-up with a Program Enabler as a parent. From a process point of view that might be an issue (citation needed) but from tools PoV this will work transparently so it's not an issue.