The Hidden God of Open Doors by Tavia Lark

Forget finding his perfect match. Rune is just desperate to talk to someone.

Rune is lonely, immortal, and trapped in a mysterious prison. Objects appear and disappear as the decades pass, and his only companions are the books and television. He hasn’t spoken to a real, live person in over two hundred years.
Until one day a phone appears, with a magical dating app already installed.
The app promises to find Rune’s perfect match for Valentine’s Day. Rune is tempted, even though he knows that’s impossible. Nobody wants a perfect match they can’t meet.
Then he matches with Raider—a confident ex-treasure hunter who shamelessly flirts past Rune’s loneliness.
And Raider doesn’t believe in impossible.