Just attache a nice pole or post to hold lights.

You could just do one on the two outer corners, then standoffs/anchors at the house, run tensioned steel cable (Feeney etc.) between the two posts, back to the house and across the house. Then string lights in any direction or pattern you want.

Wooden deck? Creating a frame, similar to a pergola, is not a ton of work. Maybe a long weekend

No, not necessarily for privacy but more that it needs some kind of framing so we can hang lights over it. I guess we could put them on the rails but I wanted an overhead light display.

Deck privacy screen.

Are you talking about boxing it in so you don't have to see the neighbors?

We have a small deck that looks out over adjacent yards and an alley. I would love to add some type of height or trellis to make it a bit cozier, so we could string lights from the house in an arc to posts (current deck railing too low), yet I don't want to re-do the whole deck in order to do something so simple. Thanks for any advice.