Hanging curtain rods - metal stud above window?

If you are only 1/2" above the opening and there is a drywall return, you are probably detecting a drywall corner bead:

It is ok to drill a pilot hole through it and send a screw right through into the wood framework.

What you have there is drywall. Without drilling a hole or tearing the drywall off, it's impossible to tell what's behind it.

Maybe turn off the "metal mode" of the stud finder, then wave it around and have it look to see if it detects any wood. If all it detects is metal then you've probably got metal studs and will have to take appropriate measures. If it detects wood, then you're 100% good to go with regular wood screws.

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Important consideration:

If you're trying to put a screw 1/2" above the corner of the drywall, you are either going to put that screw edge-on into the horizontal drywall that forms the bottom of the soffit, or you're going to put it so close to the bottom of the stud (assuming wood) that it will have effectively ZERO grip. It might even just go through the edge of the stud, tearing out the wood and effectively making a gap between the drywall and stud and not being firmly attached to anything.

Your screws may support the weight of the mount, but may collapse when you add the bar. It may support the bar, but collapse when you add the curtains. It may support the curtains, but collapse when you first open/close them. i.e. a screw with that little purchase won't hold much weight if any.

I understand that there's likely another screw above this one, but the bracket is designed with 2 screws for a reason, and that reason is to have both screws helping to hold it to something firm.