- create the widget in the Game Mode, reference it
- use the Level Blueprint as demonstrated above to hook up first actor that is manually placed in the world (providing this is a requirement - otherwise, skip this step)
- if you ever spawn new ones, replace them and so on, do so in the Game Mode and hook it up to the widget via an Event Dispatcher
Pretty much as robust as it gets. No possession necessary. No casting or interface needed if step 2 was skipped. There should be no script for this in the widget whatsoever. The widgets’ job is to show stuff, rather than finding actors that may or may not exist.