There are a few approaches to this (you've asked for option 3, but I figured I'd present some other commonly used approaches too):
Select the feature. This will keep all features visible but will highlight the one you want.
Use an AGSGraphicsOverlay to draw a copy of the feature as an AGSGraphic (perhaps with different styling). This is similar to selecting the feature but gives you more control over what and how to display. You could also consider hiding the original feature layer (using the visible property) while the graphics overlay is displayed.
Use the definitionExpression on the AGSFeatureLayer. You can either provide the attribute search used the query, or if you have the feature's ID, you can set the SQL expression to reference that ID.
